Made LVM backing disk persistent

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
2 files changed