Cpp 145

First whack at node discovery. Presently hosts are cleared after control connection is started with contact points. Control connection queries the connected node and add_host to Session to populate the list.

Creating PR for review while still running integration and leak tests.
This need to handle the additional case of we established the connection, but failed to query one of the tables. I'm thinking if we failed we could just run both queries again. The state won't be "new" anymore.