Ensure that get_iter_returns updates minions

This was getting missed previously because events containing minions and
I assume syndic (I've not seen one of those events) don't include an id.
Made the logic here more like get_cli_event_returns seen as that works.
Merge pull request #10083 from mbirtwell/fix_waiting_syndic_returns_in_salt_rc_develop

Ensure that get_iter_returns updates minions