it may happen that if the system where disk-image-create runs is busy,
then the kpartx -l run may leave a stale autodelete loop device.
This is because kpartx -l first adds a new loop device, then does the
listing and removes the loop device. The latter may not end before the
end of the kpartx run, leaving a loop device marked as autodelete.
Such kind of loop device will automatically delete itself, so the
rm -r $WORKING
after
sudo umount -f $WORKING/mnt
in the EXIT trap will fail because $WORKING does not exist anymore.
To prevent this situation, just ask udev to finish its operations,
properly removing the (temporary) loop device.
Change-Id: I12246f3dbe6b5669e698767682a5a142f803823b
626ca9ad47