registry/index: test for checking if RegistryPod uses the custom dbpath

This also resolves code sanity failure:
```
go vet ./...
tools/scripts/fetch golangci-lint 1.31.0 && tools/bin/golangci-lint run
golangci-lint missing or not version '1.31.0', downloading...
golangci/golangci-lint info checking GitHub for tag 'v1.31.0'
golangci/golangci-lint info found version: 1.31.0 for v1.31.0/linux/amd64
golangci/golangci-lint info installed /home/runner/work/operator-sdk/operator-sdk/tools/bin/golangci-lint
internal/olm/operator/registry/index/registry_pod_test.go:234:26: `containerCommandFor` - `dbPath` always receives `defaultDBPath` (`"/database/index.db"`) (unparam)
func containerCommandFor(dbPath string, items []BundleItem, hasCA bool) string {
                         ^
Makefile:122: recipe for target 'test-sanity' failed
make: *** [test-sanity] Error 1
Error: Process completed with exit code 2.
```
Signed-off-by: Amarnath Valluri <amarnath.valluri@intel.com>

internal/olm/operator/registry/index/registry_pod_test.go

@@ -91,6 +91,14 @@ var _ = Describe("RegistryPod", func() {
 				Expect(rp.DBPath).To(Equal("/database/index.db"))
 			})
 
+			It("should create a registry with custom database path", func() {
+				customDBPath := "/foo/bar/database.db"
+				rp.DBPath = customDBPath
+				output, err := rp.getContainerCmd()
+				Expect(err).To(BeNil())
+				Expect(output).Should(Equal(containerCommandFor(customDBPath, defaultBundleItems, false)))
+			})
+
 			It("should return a valid container command for one image", func() {
 				output, err := rp.getContainerCmd()
 				Expect(err).To(BeNil())