contint: proxy only enabled on wikimedia.org

The proxy configuration is server wide, which cause any virtual host to
serve them (ex: http://doc.mediawiki.org/ci/ ) when we only want to have
them served from integration.wikimedia.org.

This patch moves the proxy declaration from conf.d/ directly under the
ServerRoot where they can be included using 'Include *_proxy'.

As a side effect, that makes the bots to honor the robots.txt :-]

Change-Id: I022a3b086bb9822a9c123440d2e71d6056dafbc7
Merge "contint: proxy only enabled on wikimedia.org" into production