Make the port 'poudriere testport' clean

     - Remove ${STAGEDIR}/usr/local/www/rt42 which is unused
     - Add ${DATADIR}/{etc,lib,plugins} as empty directories: these
       are used by RT extensions.
     - Use @dir() to manage directories created under /var.  This will
       prevent the unconditional removal and replacement of the cache
       directories during updates, which results in those directories
       ending up with the wrong ownership.

PR:		195871
Submitted by:	me@nileshgr.com


git-svn-id: svn+ssh://svn.freebsd.org/ports/head@374655 35697150-7ecd-e111-bb59-0022644237b5