Add ip:port shorthand to Controller

Fixes #475

mininet/node.py

@@ -1385,6 +1385,10 @@ def __init__( self, name, inNamespace=False, command='controller',
         self.command = command
         self.cargs = cargs
         self.cdir = cdir
+        # Accept 'ip:port' syntax as shorthand
+        if ':' in ip:
+            ip, port = ip.split( ':' )
+            port = int( port )
         self.ip = ip
         self.port = port
         self.protocol = protocol