Add support for multiple cinder endpoints

Before v1 and v2 were set to the same service_type, so you could only
have one set at a time. This assumes the catalog is setup for v1
service_type 'volume' and v2 service_type 'volumev2'.

For backwards compatibility, we will allow v2 to be setup with
service_type 'volume' for existing installations.

Change-Id: Ife6d2cdb12d894b84ea3b276767fb93d487355d5