XD-476 correct the AbstractRedisRepository to delete the correct key bas...

Problem described at https://jira.springsource.org/browse/XD-476
The problem happens because when a stream created, it has the prefix for the member of a sorted order(E.g. streams.httptest). But when delete happens the prefix is not attached (only httptest passed in), which resulted the corresponding deletion silently failure. 

Corresponding unit test also created for XD-476