Master replication drain on server shutdown
Merge branch 'manu-cluster-race' into manu-replication-drain

Conflicts:
	nrv-core/src/main/scala/com/wajam/nrv/cluster/DynamicClusterManager.scala
Ensure slave do not unsubscribe when if master is leaving

The slave will unsubscribe only when the master goes down.
Merge branch 'master' into manu-replication-drain
Rename of the call-by-name drain flag for mustDrain
When shuting down the cluster, display a message with the leave result
Merge pull request #202 from wajam/manu-replication-drain

Master replication drain on server shutdown