Revert tox.ini to use old python by default
Revert tox.ini to use old python by default

Closes-Bug: #1332330

Change-Id: I824aa3f480eafdc84f45ade961dcb55200b096a3

koder-ua/nailgun-fcert,stackforge/fuel-web,zhaochao/fuel-web,SmartInfrastructures/fuel-web-dev,koder-ua/nailgun-fcert,huntxu/fuel-web,nebril/fuel-web,zhaochao/fuel-web,prmtl/fuel-web,huntxu/fuel-web,huntxu/fuel-web,zhaochao/fuel-web,nebril/fuel-web,SmartInfrastructures/fuel-web-dev,nebril/fuel-web,huntxu/fuel-web,zhaochao/fuel-web,nebril/fuel-web,prmtl/fuel-web,koder-ua/nailgun-fcert,prmtl/fuel-web,eayunstack/fuel-web,nebril/fuel-web,zhaochao/fuel-web,eayunstack/fuel-web,SmartInfrastructures/fuel-web-dev,SmartInfrastructures/fuel-web-dev,SmartInfrastructures/fuel-web-dev,huntxu/fuel-web,stackforge/fuel-web,koder-ua/nailgun-fcert,eayunstack/fuel-web,eayunstack/fuel-web,eayunstack/fuel-web,prmtl/fuel-web,stackforge/fuel-web,prmtl/fuel-web