Certificate and token generation fixes

Summary:
A few things need to be done which are on this change:

- Certificate generation should execute as an atomic operation, hence, it needs to be synchronised.
- Do not generate client token as part of certificate generation. This causes a deadlock now.
- Add more logs for troubleshooting

Reviewed By: aigoncharov

Differential Revision: D49269624

fbshipit-source-id: 071a8e5b895198730b7d914cc4622837e9094e2f

desktop/flipper-ui-browser/src/index.tsx

@@ -41,6 +41,8 @@ async function start() {
     token = manifest.token;
   }
 
+  console.info('Token is available: ' + token !== undefined && token?.length);
+
   const openPlugin = params.get('open-plugin');
   if (openPlugin) {
     function removePrefix(input: string, prefix: string): string {