gerrit-wm: Sends translatewiki events to #mediawiki-i18n

* registers gerrit::ircbot to join #mediawiki-i18n, relaying content in
  mediawiki-i18n.log
* make translatewiki and any future translatewiki/* repositories to use
  mediawiki-i18n.log
* updated tests

Test plan:

 $ cd files/gerrit/hooks
 $ python hookhelper_test.py
 ................
 ----------------------------------------------------------------------
 Ran 17 tests in 0.003s

 OK
 $

Change-Id: I5dc98959b3e06728838239e57a56e4c27f49092d