linter for our Apache configurations

Our infamous apache configuration can be subject to various typo and
mistakes.  This patch use the apache linter to load
operations/apache-config.git files based on the document root provided
by operations/mediawiki-config.git

Using the apache -C option, one can pass extra configuration arguments
such as loading some generic configuration files.

Whenever apache -t detect a syntax error, the build will fail.

Change-Id: I3ddf2fd384b2212773922d7dd980940db055498e