apache::monitoring: add diamond support; ensure mod_status is enabled

* Provision the Diamond's HttpdCollector:
  <https://github.com/BrightcoveOS/Diamond/wiki/collectors-HttpdCollector>
* Be explicit about including ::ganglia.
* Make sure mod_status is enabled.
* Include apache::monitoring in init.pp

Change-Id: I76a0d237fe7b9a44beb9b4320ace6eeac54fe754