This ticket it to investigate the relationship, potentially move around some member variables, and record in a comment why items should go in the base class vs. the sub-classes. 

The only derived classes of ClusterClientCursor are ClusterClientCursorImpl and ClusterClientCursorMock. Many member variables are stored in ClusterClientCursorImpl and ClusterClientCursorMock, but the base class ClusterClientCursor also contains a few member variables. 

It is possible that many of the member variables of ClusterClientCursorImpl could be moved to the base class to simplify things.

A possible reasoning from this discussion is that you only need to put stuff on the impl (and not the base class) if it involves taking a SCons dependency that we cannot (or don't want to) impose on all users of ClusterClientCursor. This might not be the true reason so this should be investigated.