Merge branch 'edx-west/release-merge' of github.com:edx/configuration into edx-west/release-merge-attempt-release

More tuning to recipes to get an integrated worker stack to install
properly under the new régime.

Another wip commit resolving problems installing the util stack. Also,
remove datadog from staging hosts where it's not needed.

* Making newly merged release branch get closer to working

Conflicts:
	playbooks/edx-west/carnegie-prod-app.yml
	playbooks/edx-west/prod-jumpbox.yml
	playbooks/edx-west/stage-all.yml
	playbooks/roles/common/tasks/create_users.yml (deleted)
	playbooks/roles/datadog/handlers/main.yml
	playbooks/roles/edxapp/defaults/main.yml
	playbooks/roles/edxapp/tasks/deploy.yml
	playbooks/roles/edxapp/tasks/main.yml
	playbooks/roles/nginx/tasks/main.yml
	playbooks/roles/nginx/templates/basic-auth.j2
	playbooks/roles/nginx/templates/edx_logrotate_nginx_access.j2
	playbooks/roles/nginx/templates/edx_logrotate_nginx_error.j2
	playbooks/roles/xqueue/tasks/main.yml

Go from copy to template so certs_home gets substituted in correctly

Substantially similar to the certs role developed (in paralell) that
exists on master, but this one uses pre-Croissant directory structure
and variable conventions. Modeled on the croissant-era notifier role.
Useful as a bridge to midterms, when Stanford can afford to port to the
new ways of doing things.

Includes updates to logging-related tasks for ansible and datadog. These
are ongoing problems for us at the moment.

add host for mysql

PHP / PHPMYADMIN role

Add logrotation to Stanford datadog setup

* Datadog logs now get rotated like other system logs
* nginx logs get rotated to have group syslog, so the datadog agent will
  continue to be able to read them

* Moving test() contents into doctests
* Adding comments to the methods explaining what they're used for

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
* Updates to lots of other places to make sure that their logs appear
  where we expect
* Has sample code showing how to emit events from log contents which make it
  into the Datadog event stream
* Separation of stage and prod datadog configurations