ipc: Improve teardown process

[aokblast]

1. Use shutdown before stop the thread: shutdown(2) rejects all following tx and rx but keep the fd opened. It is better than writing garbage value to the ipc server.
2. Use SleeperThread::sleep_for to prevent 2 second wait: stop() sets running status and notify the SleeperThread. As a result, we can use SleeperThread::sleep_for instead of std::thread::sleep_for to prevent wait for 2 seconds then stop