Fix setting default avatar service

Review Request #8510 - Created Oct. 30, 2016 and submitted

Barret Rennie
Review Board

When RB was updated to use the new avatar services API, this was
mistakenly updated to look up the avatar service. However, the
clean_avatar_service method does this already, so we are attempting to
lookup an item with its ID equal to the class, which isn't going to
work. This would always fail, so submitting the form would unset the
default avatar service. Reverting this fixes the issue,

Able to save the avatar services admin form and the default service gets
changed correctly.

Review Bot
David Trowbridge
Christian Hammond
Barret Rennie
Review request changed

Status: Closed (submitted)

Change Summary:

Pushed to release-3.0.x (3b13087)