tie qunit jobs to slaves

That needs a bunch of permission changes on the server. Will update
puppet. Jobs updated:

mediawiki-core-qunit
mwext-EventLogging-qunit
mwext-GuidedTour-qunit
mwext-MobileFrontend-qunit
mwext-VisualEditor-qunit

bug: 50231
Change-Id: Idd173362d8e955736682be8e31c9288d9532c50c