[core] Deflakey test advanced 9 (ray-project#35247)

Previously a bug was fixed in ray-project#33311 where pubsub causes the leak. Somehow the fix has race conditions and got triggered later when code changes.

The test is flakey because there is a race condition between raylet sending node failure and core worker exit itself.

When disconnect is sent to Raylet, Raylet will start to report worker failure. But the worker still continue to run.

GCS uses worker failure to close the connection. But if the worker is still alive, the worker might send another request the GCS which will lead to the FD leak.

Compare with ray-project#34883 it's a short term fix and the goal is to make the case the same as 2.3.

src/ray/core_worker/core_worker.cc

@@ -790,8 +790,12 @@ void CoreWorker::Exit(
          detail = std::move(detail),
          creation_task_exception_pb_bytes]() {
           rpc::DrainServerCallExecutor();
-          Disconnect(exit_type, detail, creation_task_exception_pb_bytes);
           KillChildProcs();
+          // Disconnect should be put close to Shutdown
+          // https://github.com/ray-project/ray/pull/34883
+          // TODO (iycheng) Improve the Process.h and make it able to monitor
+          // process liveness
+          Disconnect(exit_type, detail, creation_task_exception_pb_bytes);
           Shutdown();
         },
         "CoreWorker.Shutdown");
@@ -835,9 +839,13 @@ void CoreWorker::ForceExit(const rpc::WorkerExitType exit_type,
                            const std::string &detail) {
   RAY_LOG(WARNING) << "Force exit the process. "
                    << " Details: " << detail;
-  Disconnect(exit_type, detail);
 
   KillChildProcs();
+  // Disconnect should be put close to Exit
+  // https://github.com/ray-project/ray/pull/34883
+  // TODO (iycheng) Improve the Process.h and make it able to monitor
+  // process liveness
+  Disconnect(exit_type, detail);
 
   // NOTE(hchen): Use `QuickExit()` to force-exit this process without doing cleanup.
   // `exit()` will destruct static objects in an incorrect order, which will lead to