Remove duplicated shutdown method

The shutdown method on the NodeManager was duplicated, and only the main
one needed to stay. There's also no need to check if the _threadpool
attribute exists, because it always does.

This was found while working on YAN-975.

Signed-off-by: Rodrigo Tobar <rtobar@icrar.org>

daliuge-engine/dlg/manager/node_manager.py

@@ -189,11 +189,10 @@ def start(self):
         Starts any background task required by this Node Manager
         """
 
-    @abc.abstractmethod
     def shutdown(self):
-        """
-        Stops any pending background task run by this Node Manager
-        """
+        if self._threadpool:
+            self._threadpool.close()
+            self._threadpool.join()
 
     @abc.abstractmethod
     def subscribe(self, host, port):
@@ -373,11 +372,6 @@ def call_drop(self, sessionId, uid, method, *args):
         self._check_session_id(sessionId)
         return self._sessions[sessionId].call_drop(uid, method, *args)
 
-    def shutdown(self):
-        if hasattr(self, "_threadpool") and self._threadpool is not None:
-            self._threadpool.close()
-            self._threadpool.join()
-
 
 class ZMQPubSubMixIn(object):
     """