Add IControllerCompletionListener to track when the events have been consumed

...floodlightcontroller/core/IFloodlightProviderService.java

...va/net/floodlightcontroller/core/internal/Controller.java

...t/floodlightcontroller/learningswitch/LearningSwitch.java

...loodlightcontroller/core/test/MockFloodlightProvider.java