ENG-4376: Change leadership change notification from being a message
sent from the new initiator to every client interface to a message
sent from every Cartographer which sees the ZK update to the local
ClientInterface.
ENG-4376:  ClientInterface doesn't need both a LeaderCache and a
Cartographer.  Consolidate the master HSID lookup into Cartographer.
Merge pull request #395 from VoltDB/eng4376

Eng4376