ip_loadbalancer.py working now

To launch controller:
python pox.py log.level --DEBUG forwarding.ip_loadbalancer
--ip=10.0.0.250 --servers="10.0.0.3,10.0.0.4"

Launch mininet and run:
h1 arp -s 10.0.0.250 00:00:00:00:00:ff
h2 arp -s 10.0.0.250 00:00:00:00:00:ff
h3 python -m SimpleHTTPServer 80 &
h4 python -m SimpleHTTPServer 80 &
h1 wget -O - 10.0.0.250
h2 wget -O - 10.0.0.250