[Easy] Don't say we're ready until after garbage collecting

Summary:
We used to send the "Ready" event immediately before garbage
collecting. That's kind of dumb. We should say we're ready after garbage
collecting, when we're actually ready to handle a request.

This is a bigger deal when I move file watching to the monitor process,
since a ready server will just stop and wait for a message from the
monitor.

Reviewed By: samwgoldman

Differential Revision: D7336759

fbshipit-source-id: 1edaf89bcc8aa6a317ad9cc7e1cf9e6b2e0129b7

Author: gabelevi

src/server/server.ml

@@ -171,9 +171,10 @@ let process_message genv env request =
       { env with connections = Persistent_connection.remove_client env.connections client_id }
 
 let rec serve ~dfind ~genv ~env =
+  ServerPeriodical.call_before_sleeping ();
+
   MonitorRPC.status_update ~event:ServerStatus.Ready;
 
-  ServerPeriodical.call_before_sleeping ();
   let%lwt message = get_next_message () in
 
   let%lwt env = recheck_loop ~dfind genv env in