Stanford-oriented Datadog updates

* Datadog explicitly sets hostname in style Stanford uses (relies on
  /etc/hostname being accurate, requires reboot)
* Enables nginx status check module integration for datadog
* Installs nginx access log processor that counts HTTP response codes
* Supporting updates to Stanford playbooks
* Updates to lots of other places to make sure that their logs appear
  where we expect
* Has (commented-out) code to serve as example of how to emit events
  from log contents which make it into the Datadog event stream