Take another step in the direction of Apache consolidation

* Port webserver::php5 to use apache module.
* Because the apache module manages / purges /etc/apache2/sites-enabled
  recursively, there is no need to explicitly remove the default site in
  webserver::php5, so remove it.
* Get rid of webserver::apache::service and all references to it
* Add a dummy apache2 service to apache module's init.pp. I'll turn this into a
  bona fide service in the next patch, but making it a dummy here provides some
  insurance that a glitch won't cause rolling restarts of various apaches.
* Note that the app servers use neither apache nor webserver module, so the
  most mission-critical class of apaches are unaffected by this change.

Change-Id: I445322edb459995128287ca41cff6fa4ff2e6299