Update cinder backup_driver to full class name
Update cinder backup_driver to full class name

Legacy backup service support was recently dropped from cinder in
change I3ada2dee1857074746b1893b82dd5f6641c6e579 and we need to
adjust how we set the config option in devstack accordingly. This
updates the backup_driver option to specify a full class name instead
of only the module name.

Closes-Bug: #1794859

Change-Id: I3a72f38b564b8b83b233fccba7685833b6394d45

dtroyer/devstack,openstack-dev/devstack,group-policy/devstack,dtroyer/devstack,openstack-dev/devstack,group-policy/devstack,noironetworks/devstack,noironetworks/devstack,nawawi/openstack,nawawi/openstack