When we use the upstart, setup-loopback should be running as a
service to pass the salt linux.storage.loopback state
(service.running).

Change-Id: I9b19a94126b497d89bd6d05f43dca1df0304c0c6
Closes-bug: PROD-19847

This state allows to configure loopback device(s). This isn't meant to
be used in production but offers a cheap way to test Cinder with LVM
volumes.