mediawiki: consolidate hosts in site.pp, convert mw1053

Given no one is really working on the HHVM jobrunner at the moment, we
repurpose it as a HAT appserver; this also allows us to consolidate
site.pp a little bit.

Change-Id: I5a524e17f71d42e3119f6b15ddc768d8b5efcacb
Signed-off-by: Giuseppe Lavagetto <glavagetto@wikimedia.org>