Replace use of shared SingleFileStore with DummyInMemoryStore

ISPN-7286 introduced the @Store annotation, which prevents non-shareable stores from being configured as shareable. The SingleFileStore is a non-shareable store, however its exploited by certain tests with its shared configuration set to true. With the introduction of @Store, the aforementioned tests now fail with an error stating that the SingleFileStore cannot be shared.

-Therefore, it is necessary to create a SharedSingleFileStore solely for testing purposes which simply wraps the SingleFileStore and associated configurations, so that the existing tests which rely on a shared SingleFileStore do not fail. -

The DummyInMemoryStore should be used instead.