Elasticsearch: start service automatically.

The Elasticsearch service is only started when provisioning. When provisioning
is skipped (after a halt and then up), Elasticsearch would not be running.

As described in the Elasticsearch documentation we can start the service
automatically: http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/setup-service.html#_debian_ubuntu
Merge pull request #290 from madewithlove/develop

Elasticsearch: start service automatically.