code: def register_observer(observer)
        @observer_mutex.synchronize do
          log "EventListener: registering observer #{observer.class} #{observer.id}"
          @observers[observer_key_for(observer.class, observer.id)] = observer.observe_events(client)
        end
      end
docs: Register an observer instance, and start listening for events on its associated queue.
   Also ensure that we are listening for observer class update events