describe_ring should include datacenter/topology information

describe_ring is great for getting a list of nodes in the cluster, but it doesn't provide any information about the network topology which prevents it's use in a multi-dc setup. It would be nice if we added another list to the TokenRange object containing the DC information.

Optimally I could have ask any Cassandra node for this information and on the client-side prefer local nodes but be able to fail to remote nodes without requiring another lookup.