It does not happen to me on other distributions of OpenStack that
I'm testing with, so it is kinda related to the OS.
That was beaten to death in old thread
http://lists.openstack.org/pipermail/openstack-dev/2013-August/013039.html
Nice summary is in Ian's commit message
https://review.openstack.org/39862
tl;dr Debian avoids the issue by configuring its python to pip install
to /usr/local/ while Fedora/EL python maintainers refuse to diverge
from upstream, that's IIRC - I can't find rhbz with their comments,
maybe Ian will remember?
Cheers,
Alan