Support Cinder API version 2

Add support for the second version of the Cinder API, which brings
useful features such as scheduler hints, more consistent responses,
caching, filtering, etc.

Available volume services (such as 'volume' and 'volumev2') are
discovered at run time when creating the Cinder client.  Consequently,
there is not need for deployers to make a choice between API version 1
or 2, because the newest service is automatically chosen.

Implements: blueprint support-cinder-api-v2
Change-Id: If9eedd446e017a2f2a4e1b3257ff0d04834f9603
Merge "Support Cinder API version 2"