[python] fix realtimeplotapp

realtimeplotapp calls Stop() on IvyMessagesInterface and expects it to only unbind.
Add an extra Shudown method for messagesapp that also stops Ivy.

sw/lib/python/messages_tool.py

@@ -30,6 +30,9 @@ class IvyMessagesInterface():
 
     def Stop(self):
         IvyUnBindMsg(self.ivy_id)
+
+    def Shutdown(self):
+        self.Stop()
         IvyStop()
 
     def __init__del__(self):