At the moment we don't configure cinder-volume properly to deal with
ceph scenario - LVM backend is always hardcoded even for ceph scenario.
We fix this by moving cinder_backends definition from conf.d to aio
templates. With that proper tempest test has been added to verify
cinder-volume functionality.
Change-Id: I545f4098e899ab80045c9dba03101873b80f9a6c