Install, configure, and run a haproxy server.

**Role Variables**

.. zuul:rolevar:: haproxy_config_template
   :type: string
   :default: Undefined

   The config template to install for haproxy.  Must be defined.

.. zuul:rolevar:: haproxy_run_statsd
   :type: string
   :default: True

   Run the ``haproxy-statsd`` docker container to report back-end
   stats to graphite.opendev.org