Testing: Fail E2E tests when uncaught page error occurs

[aduth]

This pull request seeks to enhance end-to-end tests to fail a test if any uncaught page errors occur during their execution.

Testing instructions:

Fortunately, there are no existing page failures in existing tests. You can introduce one by adding this to edit-post/index.js in your local branch:

setTimeout( () => {
	throw new Error( 'Oops!' );
}, 1 );

Then verify that the end-to-end tests fail:

npm run test-e2e

Related resources:

• https://github.com/GoogleChrome/puppeteer/blob/master/docs/api.md#event-error
• Tests are run even when beforeAll throws error jestjs/jest#2713
• Stop testcase execution on failure in beforeEach jasmine/jasmine#577

[noisysocks]

Excellent!