Fixes#12154
The "-backup" flag before for "state *" CLI had some REALLY bizarre behavior:
it would change the _destination_ state and actually not create any
additional backup at all (the original state was unchanged and the
normal timestamped backup still are written). Really weird.
This PR makes the -backup flag work as you'd expect with one caveat:
we'll _still_ create the timestamped backup file. The timestamped backup
file helps make sure that you always get a backup history when using
these commands. We don't want to make it easy for you to overwrite a
state with the `-backup` flag.
Mitchell Hashimoto