Migrate Ceilometer Python Client to Support Keystone V3 APIs

Keystone is deprecating the V2 APIs and moving to V3 APIs. All the services'
clients are going to add support to V3 in order to smooth the transition.

Change-Id: I95875054b9f771ae89e44a061561472a76c8f4e2
Merge "Migrate Ceilometer Python Client to Support Keystone V3 APIs"