Generic volume groups support was added to Cinder in the
Newton release:
https://blueprints.launchpad.net/cinder/+spec/generic-volume-group
This is the 2nd patch that adds the tempest tests for generic
volume groups APIs in Cinder. It adds group_snapshots clients.
It adds tests for the following APIs:
* create group snapshot
* delete group snapshot
* show group snapshot
* list group snapshot
Change-Id: I21f07f7b3e8f22055e7978c0bf4aa01b80b493d9