Parameterize Dockerfiles for Open edX releases

Plumbing for ICP in the footer

We found once a minute too frequent for these for splunk

Bump to stay in sync with MMS releases

Pass these in because the defaults in docker.mk are lost

Make edx_notes_api endpoint HTTPS aware

WIP: Remove obsolete doc link settings

Determine default network interface name instead of hardcoding to eth0.

Better overridability of Graphite/Carbon configuration.

Switch to gp2 disks

They cost twice as much, but in our usage scenario this means $5/month
instead of $2.50/month and they shave several minutes off of sandbox
builds (and will probably aid other builds).

The continuous_delivery launch_instance playbook is already using gp2

Revert "Automate required vagrant plugin installation for any number of plugins."

Automate required vagrant plugin installation for any number of plugins.

Newer AMI after rabbit upgrade

Moved logic to check if plugin installation check
is necessary into vagrantplugins.rb.

Mention the internal repos

Replace `DATABASE_OPTIONS` setting

Both the automated version and non-automated version were
giving their respective plugin installation messages even
when just typing `vagrant`.

Also adjusted style on function calls.

`DATABASE_OPTIONS` was deprecated in Django 1.2 and removed in 1.4.
`OPTIONS` should now be passed as part of `DATABASES`.

Add link to testing checklist to PR template.

Instead of hardcoding to eth0.

It turns out ansible already provides info about the default network
interface in the ansible_default_ipv4 dict variable, so we can use that
instead of using the 'ip route show' command.

We previously used a less-than-optimal way of storing the configuration
values for Graphite/Carbon, which meant you had to override the entire
configuration (including restating default values, etc) to change one
thing.

This now mirrors how we approach things in the Grafana role, where each
distinct value is a distinct variable that can be overridden separately,
and is pulled together at a higher level into the configuration.

It's not a requirement and has the potentialy to appear like an actual
string, and not an empty string, which breaks things like Grafana.

Make sure NR and Splunk are available in the rabbit role

LEARNER-812