Implement graceful shutdown of agent.DataAccess (#1008)

* Implements graceful shutdown of agent.DataAccess and underlying Datastore/Logstore/MessageQueue

* adds tests for closing agent.DataAccess and Datastore

api/agent/hybrid/nop.go

@@ -58,3 +58,7 @@ func (cl *nopDataStore) GetRoute(ctx context.Context, appName, route string) (*m
 	defer span.End()
 	return nil, errors.New("Should not call GetRoute on a NOP data store")
 }
+
+func (cl *nopDataStore) Close() error {
+	return nil
+}