async _stopServer() {
        const util = require('util');
        return util.promisify(this.httpServer.stop)();
    }
### Stop Server
Does the work of stopping the server using stoppable
This handles closing connections:
- New connections are rejected
- Idle connections are closed immediately
- Active connections are allowed to complete in-flight requests before being closed

If server.shutdownTimeout is reached, requests are terminated in-flight