ZF2-446: ControllerFactories could use their own Factory Interface
Now that controller factories get a ControllerManager instead of a ServiceManager, we need to ask the ControllerManager for a it's ServiceLocator in order to get at the main ServiceManager. Problem is, a factory implementing FactoryInterface says that createService will receive a ServiceLocatorInterface which only guarantees get / has. For controller factories, createService should receive something that guarantees we can do getServiceLocator.
I'm not sure where this interface should go as the getServiceLocator method is implemented in AbstractPluginManager.