beta: make use of wgHTCPMulticastRouting

MediaWiki core received support to route HTCP requests to different
IP/port based on the purged URL:
	https://gerrit.wikimedia.org/r/#/c/4486/

The code has never been used so far but is going to be useful for beta
which has no multicast support and one cache per role.

Change-Id: Ib1a090e7f715f216fc35a139baaf0f1bf7cca703