Updated openstack/openstack
Project: openstack/neutron  42654364ac479902e2e34c6bf2505e940c28a7d9
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Have tox install via setup.py develop

tox 1.6 was released, which means that we can now take advantage of
the feature we added to it - which is using setup.py develop to
install the code into the virtualenv. The logic was taken from
run_tests.sh - so the performance issues around using tox vs. using
install_venv should now be gone.

Additionally, override the tox pip install command to avoid using
the "--pre" option which is the default in tox. "--pre" means
"Include pre-release and development versions." By default, pip will
only install stable versions of software, and that is the behavior
we want.

Change-Id: Ida5e440d1bdb9f8e9031277ea53a02d2ef171438
Co-Authored-By: Monty Taylor <mordred@inaugust.com>