Fix start/stop hanging issue on test stream service controller

The test stream controller sometimes hangs forever when the underlying grpc server start or stop in the wrong timing:

E.g., try to stop a server never started, stop a server already stopped, start a server already started and etc.

The change is to add start/stop states to handle all 6 combinations:

1. start server not started
2. start server started
3. start server stopped
4. stop server not started
5. stop server started
6. stop server stopped

So that it never hangs.