Fixes Bug 937376 - fixed hbase pool and tests

the HBasePersistentConnectionContext was not thread safe because it did not honor named connections.  It just gave out the same connection every time.  I remember talking with Tony about this long ago, and I suspect that I inadvertently lead him astray in writing this class.  

This PR replaces that class with a proper pooled connection context class with tests.

This part 1 of a series of PRs that will fix some of the issues of the middleware.