Elasticsearch: start service automatically.

Also see: https://github.com/fideloper/Vaprobash/pull/290

Note: there was no develop branch, so I did a PR to master.

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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