Copying mininet_p4 from behavioral-model repo (#86)

Updating the P4Switch class to use different mechanism
for checking when the switch is listening on the Thrift
port. This might fix an issues where Mininet hangs on
start.

P4D2_2017_Fall/utils/run_exercise.py

@@ -22,8 +22,6 @@
 import os, sys, json, subprocess, re, argparse
 from time import sleep
 
-# this path is needed to import p4_mininet.py from the bmv2 repo
-sys.path.append('/home/vagrant/behavioral-model/mininet')
 from p4_mininet import P4Switch, P4Host
 
 from mininet.net import Mininet