Add logging of Raft initialization
Tell Broker to join during 'join-cluster'
Add connection URL to Broker
Explicitly use 'raft' in URL path for Raft ops
connectionAddr -> addr

This is more line with existing Go packages.
Add protocol to Raft connection string

Fixed at HTTP for now.
Prefix remaining Raft paths with 'raft'
Check for connection URL on Broker Open()

Update unit tests suitably.
Merge pull request #1249 from otoolep/3_node_raft

Enable join of nodes to existing cluster