This change includes:
* Allow users of ceilometerclient specifying aodh_endpoint explicitly
* If aodh_endpoint didn't provided and users just provide ceilometer
endpoint and token, no auth_url, we assume aodh is unavailable and
avoid trying to get aodh endpoint.
Change-Id: Idd0ce60058d23507a99b89926e461d19db267ca2
Closes-Bug: #1488290