Add new example of making a custom Switch() class.

examples/controllers.py

+#!/usr/bin/python
+
+"""
+Create a network where different switches are connected to
+different controllers, by creating a custom Switch() subclass.
+"""
+
+from mininet.net import Mininet
+from mininet.node import OVSSwitch, Controller
+from mininet.topolib import TreeTopo
+from mininet.cli import CLI
+
+c0 = Controller( 'c0' )
+c1 = Controller( 'c1', ip='127.0.0.2' )
+cmap = { 's1': c0, 's2': c1, 's3': c1 }
+
+class MultiSwitch( OVSSwitch ):
+    "Custom Switch() subclass that connects to different controllers"
+    def start( self, controllers ):
+        return OVSSwitch.start( self, [ cmap[ self.name ] ] )
+
+topo = TreeTopo( depth=2, fanout=2 )
+net = Mininet( topo=topo, switch=MultiSwitch, build=False )
+net.controllers = [ c0, c1 ]
+net.build()
+net.start()
+CLI( net )
+net.stop()