Run the check_job_queue check only on terbium

Instead of tying the job queue check with the
role::applicationserver::maintenance class and hence have it run from
all kinds of places (incl. pmtpa hosts, from which it timed out), run it
explictly on terbium.

This moves an icinga:: class inside site.pp, which is ugly, but not much
uglier than having an icinga:: class under role/applicationserver.pp.
terbium has tons of misc::maintenance classes too, so we can rethink
about moving the contents of icinga::monitor::jobqueue into one of the
refactored maintenance host classes, when we get to do that..

Change-Id: Icaa523fa7ef2b07cb731179bd69c42e9c489aad5