Fix behavior when config_guestUserAutoCreated=true

 - Show "Resetting guest..." indicator when guest is being auto-created

 - If guest fails to auto-create, call refreshUsers() so that we show
   "Guest" instead of "Add guest"

Test: With config_guestUserAutoCreated=true, switch to guest, then
      select reset guest. Ensure that QS shows "Resetting guest..."
      momentarily and then switchs to "Guest"
Test: Repeat steps above, but replace newGuestId = createGuest() with
      newGuestId = UserHandle.USER_NULL in scheduleGuestCreation(), and
      add a call to Thread.sleep(5000). Ensure the result is the same.
Bug: 191990886
Change-Id: Ie27acacf83842d381e2dc5100267278659053dca