Add StateListener.onLocationUpdated (JAVA-315 #send-to-testing).

:warning: **Depends on pcmanus/ccm#128**

As discussed in the issue comments, I've added the method to `StateListener` rather than `LoadBalancingPolicy`. If we decide that it's better to keep it only on the former, I can make the change quickly.

Currently, `onLocationUpdated` can be called before `onAdd` when a new node is added. I've mentioned that in the javadocs, I think listener implementations can easily deal with it. However, it could be handled in the code by passing the node's state (new or not), I just thought it wasn't worth the effort. Again, I can add that if needed.