Comment 3 for bug 1274135

After merging the above patch, downgrading tox and virtualenv on the slaves was somewhat messy since pip uninstall was not cleaning up after itsef. The downgrade was eventually successfully accomplished with:

sudo salt '*.slave.openstack.org' cmd.run '
    sudo pip uninstall --yes tox virtualenv
    sudo rm -rf /tmp/pip-build-* /usr/local/lib/python2.7/dist-packages/tox \
        /usr/local/lib/python2.7/dist-packages/virtualenv \
        /usr/local/bin/tox /usr/local/bin/virtualenv
    sudo pip install -U tox==1.6.1 virtualenv==1.10.1'

(Well, almost... I special-cased the precisepy3k slaves to s/pip/pip3/ and s/2.7/3.3/ but otherwise the same.)