Try to bind /cow to /live/cow if unable to move.

* This should re-enable using of live-snapshot with targets differents
  from static list cpio's.

Signed-off-by: Marco Amadori <amadorim@vdavda.com>

scripts/live

@@ -1173,7 +1173,7 @@ setup_unionfs ()
 
 	# shows cow fs on /cow for use by live-snapshot
 	mkdir -p "${rootmnt}/live/cow"
-	mount -o move /cow "${rootmnt}/live/cow"
+	mount -o move /cow "${rootmnt}/live/cow" || mount -o bind /cow "${rootmnt}/live/cow" || [ "${quiet}" != "y" ] && log_warning_msg "Unable to move or bind /cow to ${rootmnt}/live/cow"
 }
 
 check_dev ()