Comment 2 for bug 1478480

@Steve Baker:
Thanks, in fact, there is another problem, if we update with the invalid subnet again(instead of the above step5), even if after this change( correct the stack identity), the stack will be UPDATE_FAILED, but the instance has been deleted, I think user will confuse this result. So how to solve this problem, why we delete the backup resource in second update not in first update? why we delete the backup resource before the new one be created successful?