Add tox to test-requirements.txt
Add tox to test-requirements.txt

Change-Id: I0f4e1a28149dee06f6e8496b68fb4bc518c108b1
Closes-bug: #1333789

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