Comment 1 for bug 1723216

As of systemd 211 (i.e. >= vivid), the default udev rules arrange to not create loop devices. In older releases, udev creates those, but we can race with it on startup.

I think we need to:

 * wait until the container has done more of its startup work before proceeding
 * check whether /dev/loop* exist before creating them

Neither of these is sufficient on its own.