Remove volume client and usage in scenario tests

We don't need the volume/Cinder client in our scenario
tests, nor the methods that it was currently being
used in. Remove its usage from the base class to
unblock https://review.openstack.org/#/c/573135/

Change-Id: I111c648280912fcbad671cc27cf87c496e8689ba
Needed-By: https://review.openstack.org/#/c/573135/
1 file changed