refact(controller): Decouple listeners/servers shutdown from Worker

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.

internal/servers/controller/testing.go

@@ -279,7 +279,7 @@ func (tc *TestController) Shutdown() {
 	tc.cancel()
 
 	if tc.c != nil {
-		if err := tc.c.Shutdown(false); err != nil {
+		if err := tc.c.Shutdown(); err != nil {
 			tc.t.Error(err)
 		}
 	}