Shutdown command

Summary:
Introduce a 'shutdown' command which effectively kills the process.

Killing the process, for flipper-server, will close down the server and active ws connections.

Reviewed By: passy

Differential Revision: D37209193

fbshipit-source-id: 83303e8209530a41ba870009603cfb383915b7a6

desktop/flipper-server-core/src/FlipperServerImpl.tsx

@@ -478,6 +478,9 @@ export class FlipperServerImpl implements FlipperServer {
       return internGraphGETAPIRequest(endpoint, params, options, token);
     },
     'intern-upload-scribe-logs': sendScribeLogs,
+    shutdown: async () => {
+      process.exit(0);
+    },
   };
 
   registerDevice(device: ServerDevice) {