Previously, loop devices for LVM volume groups backing files were not
created after reboots, causing e.g. Cinder to fail with messages such
as
ERROR cinder.service [-] Manager for service cinder-volume
devstack@lvmdriver-1 is reporting problems, not sending
heartbeat. Service will appear "down".
Now, we use systemd services to manage loop devices for backing files.
Change-Id: I27ec027834966e44aa9a99999358f5b4debc43e0