Remove "from __future__ import print"

This was well-intentioned, but it causes more trouble
than it's worth.

Fixes #652

examples/test/test_sshd.py

@@ -4,7 +4,6 @@
 Test for sshd.py
 """
 
-from __future__ import print_function
 import unittest
 import pexpect
 from mininet.clean import sh