Only delete an expired snapshot if there's an automatic task in the database that created it.

Ticket: #5305

If you are manually copying snapshots around that FreeNAS created and they encounter
another FreeNAS box it will happily delete them because the name regex matches.
(If they are past the expiration date, which is hardcoded in the name)

This commit addresses that behavior such that FreeNAS will not
delete "foreign" snapshots based on the name alone.