In general, these changes were introduced in the same vein of the
changes to controller `startListeners`.
Specifically, these changes also decouple the Controller and the Worker
shutdown processes. Currently, a call to `stopListeners` on an instance
that is running as both a Controller and a Worker would stop the
listeners for both.
Lastly, we also add unit/integration tests to the shutdown code.
Hugo Vieira
eebdfb88dc