Hello, I'm trying to run tox tests on nova. Every test passes fine, but pip-missing-reqs fails:

tox -e pip-missing-reqs

Traceback (most recent call last):
  File "/root/nova/.tox/pip-missing-reqs/bin/pip-missing-reqs", line 7, in <module>
    from pip_missing_reqs.find_missing_reqs import main
  File "/root/nova/.tox/pip-missing-reqs/local/lib/python2.7/site-packages/pip_missing_reqs/find_missing_reqs.py", line 14, in <module>
    from pip.utils import get_installed_distributions, normalize_name
ImportError: cannot import name normalize_name
ERROR: InvocationError: '/root/nova/.tox/pip-missing-reqs/bin/pip-missing-reqs -d --ignore-file=nova/tests/* --ignore-file=nova/test.py nova'
___________________________________________________________________________________________________________________________________ summary ___________________________________________________________________________________________________________________________________
ERROR:   pip-missing-reqs: commands failed

pip --version pip 9.0.1 from /usr/local/lib/python2.7/dist-packages (python 2.7)

This happens on Debian Jessie, Ubuntu Trusty and Ubuntu Xenial. Any ideas, what's wrong? Thank you.