Add support for django-statsd

This changeset adds django-statsd support and middleware integration in
all environments. The middleware automatically emits metrics for model
interactions, HTTP response codes, and view rendering timers. Additional
metrics can be emitted via:

  from django_statsd.clients import statsd

  # Increments the "something_interesting" counter by 1
  statsd.incr('something_interesting')

Metrics flow through:

  Django (app) -> Statsite (services) -> Graphite (services)

Attempts to resolve #16.
Add monitoring variables for test environment

The test provisioning path does not include monitoring since #52, but
when monitoring specific attributes are not set, they render as:

{# statsite_host #}

This breaks client attempts at DNS resolution.

This changeset populates valid monitoring specific attributes so that
attempts at DNS resolution don't fail.
Merge branch 'feature/hmc/django-statsd' into develop