Don't setup identity v3 client if v3 is disabled

Some tests report failures about the identity v3 url not being
specified, even if api_v3 is set to false in tempest.conf.

Change-Id: Ifb5c6c8bd154373d33c90236ff37fcc5b8759405
Closes-Bug: #1389742
Fixes volume client in volume tests

volumes_client is coming from cls.os and volume_client is coming
from cls.os_adm. Here it creates a naming disaster for the volume
client. Adding admin_volume_client at the place of volume_client
fixes the client for admin user.

Change-Id: I0c55d3f7fbf4a096c012ffee3697f14869fe9962
Fix tox stress invocation to not quote arguments

Change-Id: I6fc1e64c3e52a02126235d5cc42831ee2d25f997
Merge "Don't setup identity v3 client if v3 is disabled"
Merge "Fixes volume client in volume tests"
Merge "Fix tox stress invocation to not quote arguments"