Adds set_config to the ECS supported methods.

This branch adds hierarchical command functionality to the ECS along with the set_config env method.

__To QA__
- Open the GUI using the `ecs` flag.
- Drag the liferay from the charmbrowser and click the deploy button once.
- Open the console and run `app.ecs.changeSet` and make note of the id (service-xxx).
- Run the following substituting the id with the appropriate one `app.ecs.setConfig('service-xxx', {'http-port': "80802"}, null, {'http-port': "8080"}, function() {});`.
- Run `app.ecs.changeSet` and there should now be two entries in the 'commands' array the second of which should have the method property set to 'set_config'.