added shutdown to mgen actor

From: macker

daemon/core/services/nrl.py

@@ -588,7 +588,7 @@ class MgenActor(NrlService):
     # list of startup commands, also may be generated during startup
     _startup = ("sh start_mgen_actor.sh", )
     # list of shutdown commands
-    _shutdown = ()
+    _shutdown = ("killall mgen")
     @classmethod
     def generateconfig(cls, node, filename, services):
         ''' Generate a startup script for MgenActor. Because mgenActor does not