Change the site-include regexp to work better with Debian/Ubuntu...

...as it is commonly used practice to omit the '.conf' part on vhost files.

When the puppetmaster is deployed using passenger it will break with after using the apache module because of the site-include regexp requiring a '.conf' ending for all vhosts. The puppetmaster vhost however has no '.conf' ending and will be omitted when apache is reloading/restarting.