Support for Shield

[simonclausen]

I view shield as a core functionality of Elasticsearch and think it makes sense to have a discussion about how this formula could/should support the configuration.

Most other plugins can be configured via elatsicsearch.yml, but Shield requires more than what is available today, ranging from distribution of roles.yml to installation of the json license.

Should this functionality be separated into it's own state, e.g. elasticsearch.shield (x-pack from version 5 onward), or does it make sense to include it in the elasticsearch.config state?