Grab-bag of mediawiki_singlenode tuneups.

- Add $mysql_pass argyment
- Avoid duplicate definitions of webserver::php5
- Avoid duplicate definitions of memcached
- Remove unused symlink to /var/www
- Rename 'controller' to 'wikicontroller' to prevent naming conflicts
- Increase use of $install_path

Change-Id: I6c4caa12223746af5860532cad0281b064df2f14