Specify AZ for non-scenario tests

The review allows related non-scenario tests which create
volumes and servers to read and use
CONF.compute.compute_volume_common_az.
If the tests don't use the option and tested environment has
multiple availability_zones, the tests fail.

Related-bug: #1647999

Change-Id: Ia0a6fd2175635d4375514d7609646b4516836dc0
3 files changed