restore-single-files: reduce chance of UUID collision

XFS can't mount multiple images that happen to have the same UUID.
This can happen either due to PL-132849 or if you'd like to restore
from multiple revisions of the same disk.

This change reduces the chance by changing the UUID during restore.
However, there's a small mount/umount cycle with the old UUID that
could collide, but xfs needs a clean log to change the UUID.

Re PL-132849

pkgs/restore-single-files/restore-single-files.sh

@@ -56,6 +56,13 @@ while [ ! -e $LOOPPART ]; do
 	sleep 0.2
 done
 
+info "Pre-mounting image to flush log"
+mount -oloop ${LOOPPART} $LOOPMNT
+umount $LOOPMNT
+
+info "Regenerating UUID to avoid collisions"
+xfs_admin -U generate ${LOOPPART}
+
 info "Mounting image"
 mount -oloop ${LOOPPART} $LOOPMNT