Consider using the resource name as a common shared set of resources

[martinb3]

Consider using the resource's name to look up other resources in the collection, and share default values. For example, if elasticsearch_user 'foo' has been defined, elasticsearch_configure 'foo' would look up the group parameter from elasticsearch_user 'foo' instead of requiring the user to provide/override it.

The downside of this design is that things like elasticsearch_plugin 'head' would no longer work, as it would try to use head as the instance name instead of the plugin name.