Updated openstack/openstack
Project: openstack/python-novaclient  6d18987223208de85b9bc4eb174240023a9b4ff3

Propose 'tox' as tests launcher

Since ``tox`` is used as launcher in gates, it should be mentioned in docs
instead of ``python setup.py test``.

Change-Id: Ie5fcd9da755e1146b2b042fa5906aa28748980a6