Reduce gerritadmin traffic a bit by ignoring ASSIGNED->PATCH_TO_REVIEW

Unfortunately gerritadmin has to make its 'new patch' comment in a
separate API request to modifying the status, due to BZ API limitations.

I'd prefer that the bot was a little quieter about this, so this
patch suppresses the (IMO) less helpful of the two changes

(Untested)
refactor gerrit status change check into seperate function

Change-Id: Ia49c587909e973d5862ab4badb45e78f9870eab1