Re-use common methods in test_delete_server_while_in_attached_volume
Re-use common methods in test_delete_server_while_in_attached_volume

This changes the test_delete_server_while_in_attached_volume test
to re-use common volume create/attach methods in the base compute
API test class.

Note that this changes the volumes client used to create, get and
delete the volume. The test was previously using the proxy volumes
extension from the compute API which is now deprecated.

Change-Id: Ief13602a6764c3259a827d6d2a4c40436f04667a

vedujoshi/tempest,cisco-openstack/tempest,vedujoshi/tempest,masayukig/tempest,openstack/tempest,Tesora/tesora-tempest,cisco-openstack/tempest,sebrandon1/tempest,sebrandon1/tempest,openstack/tempest,Juniper/tempest,Tesora/tesora-tempest,Juniper/tempest,masayukig/tempest