Connectivity between the endpoint version and OS_VOLUME_API_VERSION.

Adds functionality which allows user to work with
that cinder API version which is the same as
the endpoint version.

Fixes: bug #1169455

Change-Id: I9bb46e602d15856d2da502a6ac2b6c25e76f4fa3
Merge "Connectivity between the endpoint version and OS_VOLUME_API_VERSION."