Add skeleton logstash module.

This new logstash module adds classes to install logstash agents and
indexers as well as redis and elasticsearch. The configuration for each
of these services is rudimentary but it shouldn't be difficult to expand
the configs and make them useful.

Also, add a logstash.openstack.org node that will have an agent,
indexer, web frontend, redis, and elasticsearch installed on it.

Change-Id: I25b635f088f99d45cfaa70ed122c6433d3784937
Reviewed-on: https://review.openstack.org/19871
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Approved: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Tested-by: Jenkins