CPULimitedHost cleanup() calls superclass method

fixes #161

mininet/node.py

@@ -619,6 +619,7 @@ def popen( self, *args, **kwargs ):
         return Host.popen( self, *args, mncmd=mncmd, **kwargs )
 
     def cleanup( self ):
+        super(CPULimitedHost, self).cleanup()
         "Clean up our cgroup"
         retry( retries=3, delaySecs=1, fn=self.cgroupDel )