Add test_get_all_by_volume in objects/test_backup
Add test_get_all_by_volume in objects/test_backup

Rename test_get_all_for_volume to test_get_all_by_host.

There is a get_all_by_volume in the backup, but it has no
test_get_all_by_volume in the test_backup.Therefore, I add it.

Change-Id: I68109402dd354a3a3e03bd81240ad451b873bc10

phenoxim/cinder,cloudbase/cinder,cloudbase/cinder,mahak/cinder,Hybrid-Cloud/cinder,Datera/cinder,openstack/cinder,j-griffith/cinder,Hybrid-Cloud/cinder,eharney/cinder,mahak/cinder,ge0rgi/cinder,phenoxim/cinder,openstack/cinder,NetApp/cinder,NetApp/cinder,eharney/cinder,Datera/cinder,j-griffith/cinder