Work aaround apparent tox bug where package wasn't being installed.
Work aaround apparent tox bug where package wasn't being installed.

Bug report: https://bitbucket.org/hpk42/tox/issues/176/tox-doesnt-install-the-package-being

projectcalico/python-posix-spawn,projectcalico/python-posix-spawn,Metaswitch/posix_spawn,projectcalico/python-posix-spawn,Metaswitch/posix_spawn,Metaswitch/posix_spawn