Replace references to /u/l/a/common-local with /srv/mediawiki

* Change the default target directory to /srv/mediawiki (we already set it to
  that in scap.cfg, so this should be a no-op.
* Change a path reference in scap-recompile, too.

Change-Id: I5d63e486bbc0cd691f09cd4bdc419ee4130fd362