Isolate integration tests from CPP API

The following discussion from !153 (merged) should be addressed:

• @jgrogan started a discussion: (+1 comment)

  This is ok for now - but just in case using the existing tests as a reference, ideally we don't want this CppClientTestWrapper to spread too much. We should just be testing the RedisKeyValueStoreClient directly where possible - otherwise when we change anything else in the code we can affect this test - it makes maintenance difficult.