zuul: suffix mw testextension jobs with '-zend'

Jobs created earlier. Also add the '-hhvm' jobs albeit commented out for
now.

This cause the first build of the job on an instance to lag out by 3+
minutes as mediawiki/core is being cloned.

Once deployed, we can drop the unprefixed jobs to reclaim disk space.

Bug: T75521
Change-Id: Ic9c7b057a62b49f09775cd0815ebf02ee526a326