Updated SimpleDBConsumedStoreTest

Added test for method to retrieve entriesToBeConsumed
Refactored existing methods
Fixed Mock initialization in FeedConsumerImplTest
Replaced ConsumedStore type variable with hard type

In one place the generic interface was passed a parameter of a different type. It compiled because in that instance the type variable was left unbound. But at runtime it caused the thread to hang-up without throwing any exception...
The problem was causing the MultipleClientTest to misbehave.