Add metrics for server cert generation and server start

Summary: Will provide some visibility on error rates.

Reviewed By: passy

Differential Revision: D13671492

fbshipit-source-id: 60971a7e8163c58dd4d6540e57e05b38c852744e

src/server.js

@@ -71,6 +71,7 @@ export default class Server extends EventEmitter {
         this.insecureServer = this.startServer(INSECURE_PORT);
         return;
       });
+    recordSuccessMetric(this.initialisePromise, 'initializeServer');
     return this.initialisePromise;
   }