mw/ext/wikibase now has gate-and-submit

The catch all unit tests job was not properly working since the Wikibase
extension has several sub extensions.  Instead it is now tested by two
different job, one known as 'repo' the other as 'client'.

Enable gate-and-submit and use 'repo' as sole unit tests which is better
than nothing.

Change-Id: I972b51ebfb3588e741fa46455ef2e5d3b06fd956