Don't stop data network controllers twice.

examples/controlnet.py

@@ -107,6 +107,8 @@ def __init__( self, n, dataController=DataController, **kwargs ):
 net.stop()
 
 info( '* Stopping Control Network\n' )
+# dataControllers have already been stopped
+cnet.hosts = list( set( cnet.hosts ) - set( dataControllers ) )
 cnet.stop()