tox: Add py34 target
tox: Add py34 target

Add support for python 3.4.

Change-Id: Ie85ecb09fdf0758226e119f63db60c2696ab84c2
Signed-off-by: Kyle Mestery <9cfbda34e625c7b0454bcb19a48d07c46f9097d2@mestery.com>

FrankDuan/df_code,neoareslinux/dragonflow,openstack/dragonflow,neoareslinux/dragonflow,openstack/dragonflow,FrankDuan/df_code,openstack/dragonflow,FrankDuan/df_code