Revert "Shutdown request handler before network server in ambry server (

#1206)" (#1273)

This reverts commit 063ca5e.
We have some suspicions that the frontend may not be able to deal with
this nicely if it is in the middle of writing to a socket.

ambry-server/src/main/java/com.github.ambry.server/AmbryServer.java

@@ -221,12 +221,12 @@ public void shutdown() {
       if (statsManager != null) {
         statsManager.shutdown();
       }
-      if (requestHandlerPool != null) {
-        requestHandlerPool.shutdown();
-      }
       if (networkServer != null) {
         networkServer.shutdown();
       }
+      if (requestHandlerPool != null) {
+        requestHandlerPool.shutdown();
+      }
       if (replicationManager != null) {
         replicationManager.shutdown();
       }