Add a playbook for installing and configuring Graphite.

This playbook will install carbon-cache and graphite-api to provide a
minimalistic starting point for metrics collection.

It currently installs all components from their upstream source (albeit
with defaults that point to tags, and not master/development branches).
It uses systemd, and so is tailored specifically to Ubuntu 16.04.

It currently does not support any of the advanced configuration such as
multiple carbon-cache process + carbon-relay.  It is also lacking many
variables to fully tweak the various configuration files, although
there's support for fully configuring the storage schemas.

There is a small "master" playbook -- edx-monitoring -- for running the
role, and in the future, supporting the culmination of other playbooks
to build out an all-in-one monitoring server: Graphite, Grafana, etc.

Update to the latest awscli.

Add an ec2 related plugin

This avoids running the entire role if you just want one new plugin.
It intentionally makes you restart Jenkins so you can put it in quiet
mode, wait out any jobs and then restart.

Also address prior nit regarding grouping plugins by usage

Prompted because the awscli on go-agents needs to be above 1.10.47 to be
able to take advantage of IAM roles for tasks automatically.

Explicitly allow read access to gocd log directory.

We now make use of the management command's initial-only flag silently exit if the countries table is already populated.

ECOM-7422

We don't use this bot.

updated migration rollback docs

Switch from git_add_course to standard import

Adds ANALYTICS_API_AGGREGATE_PAGE_SIZE, default value 10

git_add_course uses the platform's sysadmin dashboard which assumes it
can create an xlog mongo database and write into it without auth
configured.  This is not something we want to spend more time enabling,
so switch to our 'standard' import technique.

This relies on the demo role more than I would like, but we have a
backlog task to clean that role up, and can touch this at the same time
(this role has always imported a bunch of vars from demo, so I'm not
 adding any new deps).

Allow for a list of users that have credentials.

Added monitoring tag to rabbitmq ansible

and CHANGELOG entry.

Leaving the old vars here for compatibilty.  They can be removed at some future time.

We don't need a separate fullstack installation any more

sync the locust role with edx-load-tests

ECOM-7207

* Do not start locust automatically, instead make the locust user
  suitable for interactive manipulation and execution of the codebase.
  This works well for the current iteration of edx-load-tests which
  expects the user to hand-modify settings files.

* For convenience, the locust user gets dropped straight into the
  edx-load-tests codebase and sources a virtualenv with most
  dependencies already installed.

* Add an extra MOTD related to loadtesting

PERF-415

Improve docs and become www-data

I see no reason for us not to retry

The continuous-deliver/ playbooks are already doing this.

mattdrayer/ENT-244: Add ENTERPRISE_SERVICE_URL setting

mattdrayer: Remove ENTERPRISE_API_URL setting

Change the default XQUEUE_RABBITMQ_TLS value to false

We didn't need this previously, so I'm a little concerned by it.
Tweaked as part of DEVOPS-5543

rabbitmq memory alerting