fix(jasmine): unhanded promise rejection causes tests suit to pass

Currently unhandled promise rejection caused tests suit to pass. Example:
```
yarn bazel test //packages/angular_devkit/core:core_test --test_summary=detailed --test_output=all
INFO: Analyzed target //packages/angular_devkit/core:core_test (2 packages loaded, 148 targets configured).
INFO: Found 1 test target...
Target //packages/angular_devkit/core:core_test up-to-date:
  dist/bin/packages/angular_devkit/core/core_test.sh
  dist/bin/packages/angular_devkit/core/core_test_loader.js
  dist/bin/packages/angular_devkit/core/core_test_require_patch.js
INFO: Elapsed time: 0.357s, Critical Path: 0.02s
INFO: 1 process: 1 internal.
INFO: Build completed successfully, 1 total action
PASSED: //packages/angular_devkit/core:core_test (see /private/var/tmp/_bazel_alanagius/5168427e57f204ca069c602aa7ed1931/execroot/angular_cli/bazel-out/darwin-fastbuild/testlogs/packages/angular_devkit/core/core_test/test.log)
INFO: From Testing //packages/angular_devkit/core:core_test
==================== Test output for //packages/angular_devkit/core:core_test:
(node:11987) UnhandledPromiseRejectionWarning: Error: Cannot find module '/private/var/tmp/_bazel_alanagius/5168427e57f204ca069c602aa7ed1931/execroot/angular_cli/node_modules/@angular-devkit/core/src/index.js'. Please verify that the package.json has a valid "main" entry
    at tryPackage (internal/modules/cjs/loader.js:303:19)
    at Function.Module._findPath (internal/modules/cjs/loader.js:516:18)
    at Function.Module._resolveFilename (internal/modules/cjs/loader.js:867:27)
    at Function.Module._load (internal/modules/cjs/loader.js:725:27)
    at Module.require (internal/modules/cjs/loader.js:952:19)
    at require (internal/modules/cjs/helpers.js:88:18)
    at Object.<anonymous> (packages/angular_devkit/core/src/virtual-fs/host/memory_spec.ts:10:1)
    at Module._compile (internal/modules/cjs/loader.js:1063:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1092:10)
    at Module.load (internal/modules/cjs/loader.js:928:32)
    at Function.Module._load (internal/modules/cjs/loader.js:769:14)
    at Module.require (internal/modules/cjs/loader.js:952:19)
    at require (internal/modules/cjs/helpers.js:88:18)
    at Loader.requireShim [as require_] (node_modules/jasmine/lib/loader.js:35:3)
    at node_modules/jasmine/lib/loader.js:28:12
    at new Promise (<anonymous>)
    at Loader.load (node_modules/jasmine/lib/loader.js:27:12)
    at Jasmine.loadSpecs (node_modules/jasmine/lib/jasmine.js:91:23)
    at Jasmine.execute (node_modules/jasmine/lib/jasmine.js:267:3)
(Use `node --trace-warnings ...` to show where the warning was created)
(node:11987) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 2)
(node:11987) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
================================================================================
Test cases: finished with 1 passing and 0 failing out of 1 test cases
Executed 0 out of 1 test: 1 test passes.
```

The reason for this is because Jasmine `execute` method returns a `Promise`, which was not handled properly. See: https://unpkg.com/browse/jasmine@3.7.0/lib/jasmine.js#L267

Without this fix

```
yarn bazel test //packages/angular_devkit/core:core_test
yarn run v1.22.10
INFO: Build options --action_env and --enable_runfiles have changed, discarding analysis cache.
INFO: Analyzed target //packages/angular_devkit/core:core_test (3 packages loaded, 6322 targets configured).
INFO: Found 1 test target...
Target //packages/angular_devkit/core:core_test up-to-date:
  dist/bin/packages/angular_devkit/core/core_test.sh
  dist/bin/packages/angular_devkit/core/core_test_loader.js
  dist/bin/packages/angular_devkit/core/core_test_require_patch.js
INFO: Elapsed time: 7.172s, Critical Path: 6.58s
INFO: 4 processes: 2 local, 2 worker.
INFO: Build completed successfully, 4 total actions
//packages/angular_devkit/core:core_test                                 PASSED in 0.5s

Executed 1 out of 1 test: 1 test passes.
INFO: Build completed successfully, 4 total actions
```

With this fix:
```
yarn bazel test //packages/angular_devkit/core:core_test
yarn run v1.22.10
$ /Users/alanagius/git/angular-cli/node_modules/.bin/bazel test //packages/angular_devkit/core:core_test
INFO: Analyzed target //packages/angular_devkit/core:core_test (1 packages loaded, 10 targets configured).
INFO: Found 1 test target...
FAIL: //packages/angular_devkit/core:core_test (see /private/var/tmp/_bazel_alanagius/5168427e57f204ca069c602aa7ed1931/execroot/angular_cli/bazel-out/darwin-fastbuild/testlogs/packages/angular_devkit/core/core_test/test.log)
INFO: From Testing //packages/angular_devkit/core:core_test:
==================== Test output for //packages/angular_devkit/core:core_test:
[jasmine_runner.js] An error has been reported: Error: Cannot find module '/private/var/tmp/_bazel_alanagius/5168427e57f204ca069c602aa7ed1931/execroot/angular_cli/node_modules/@angular-devkit/core/src/index.js'. Please verify that the package.json has a valid "main" entry
    at tryPackage (internal/modules/cjs/loader.js:303:19)
    at Function.Module._findPath (internal/modules/cjs/loader.js:516:18)
    at Function.Module._resolveFilename (internal/modules/cjs/loader.js:867:27)
    at Function.Module._load (internal/modules/cjs/loader.js:725:27)
    at Module.require (internal/modules/cjs/loader.js:952:19)
    at require (internal/modules/cjs/helpers.js:88:18)
    at Object.<anonymous> (packages/angular_devkit/core/src/virtual-fs/host/memory_spec.ts:10:1)
    at Module._compile (internal/modules/cjs/loader.js:1063:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1092:10)
    at Module.load (internal/modules/cjs/loader.js:928:32)
    at Function.Module._load (internal/modules/cjs/loader.js:769:14)
    at Module.require (internal/modules/cjs/loader.js:952:19)
    at require (internal/modules/cjs/helpers.js:88:18)
    at Loader.requireShim [as require_] (node_modules/jasmine/lib/loader.js:35:3)
    at node_modules/jasmine/lib/loader.js:28:12
    at new Promise (<anonymous>)
    at Loader.load (node_modules/jasmine/lib/loader.js:27:12)
    at Jasmine.loadSpecs (node_modules/jasmine/lib/jasmine.js:91:23)
    at Jasmine.execute (node_modules/jasmine/lib/jasmine.js:267:3)
    at main (node_modules/@bazel/jasmine/jasmine_runner.js:157:3)
    at node_modules/@bazel/jasmine/jasmine_runner.js:182:26 {
  code: 'MODULE_NOT_FOUND',
  path: '/private/var/tmp/_bazel_alanagius/5168427e57f204ca069c602aa7ed1931/execroot/angular_cli/node_modules/@angular-devkit/core/package.json',
  requestPath: '@angular-devkit/core'
}
================================================================================
Target //packages/angular_devkit/core:core_test up-to-date:
  dist/bin/packages/angular_devkit/core/core_test.sh
  dist/bin/packages/angular_devkit/core/core_test_loader.js
  dist/bin/packages/angular_devkit/core/core_test_require_patch.js
INFO: Elapsed time: 0.761s, Critical Path: 0.42s
INFO: 2 processes: 2 local.
INFO: Build completed, 1 test FAILED, 2 total actions
//packages/angular_devkit/core:core_test                                 FAILED in 0.4s
  /private/var/tmp/_bazel_alanagius/5168427e57f204ca069c602aa7ed1931/execroot/angular_cli/bazel-out/darwin-fastbuild/testlogs/packages/angular_devkit/core/core_test/test.log
```

Closes #2688

packages/jasmine/jasmine_runner.js

@@ -61,7 +61,7 @@ function readArg() {
   return process.argv.splice(2, 1)[0];
 }
 
-function main(args) {
+async function main(args) {
   if (args.length < 2) {
     throw new Error('expected argument missing');
   }
@@ -133,7 +133,7 @@ function main(args) {
     // Patch the inner execute function to do our filtering first.
     const env = jasmine.getEnv();
     const originalExecute = env.execute.bind(env);
-    env.execute = () => {
+    env.execute = async () => {
       const allSpecs = getAllSpecs(env);
       // Partition the specs among the shards.
       // This ensures that the specs are evenly divided over the shards.
@@ -144,7 +144,7 @@ function main(args) {
       const end = allSpecs.length * (SHARD_INDEX + 1) / TOTAL_SHARDS;
       const enabledSpecs = allSpecs.slice(start, end);
       env.configure({specFilter: (s) => enabledSpecs.includes(s.id)});
-      originalExecute();
+      await originalExecute();
     };
     // Special case!
     // To allow us to test sharding, always run the specs in the order they are declared
@@ -154,7 +154,8 @@ function main(args) {
     }
   }
 
-  jrunner.execute();
+  await jrunner.execute();
+
   return 0;
 }
 
@@ -176,5 +177,12 @@ function getAllSpecs(jasmineEnv) {
 }
 
 if (require.main === module) {
-  process.exitCode = main(process.argv.slice(2));
+  (async () => {
+    try {
+      process.exitCode = await main(process.argv.slice(2));
+    } catch (error) {
+      console.error('[jasmine_runner.js] An error has been reported:', error);
+      process.exitCode = 1;
+    }
+  })();
 }