Throw meaningful error when trying to use a closed Cluster (JAVA-335 #send-to-testing).
Merge pull request #182 from olim7t/java335

JAVA-335: throw meaningful error when trying to use a closed Cluster.
Add StateListener.onLocationUpdated (JAVA-315).

The goal is to avoid calling onDown + onUp on the LoadBalancingPolicy
when only the location (datacenter and/or rack) of a node has changed.