devstack-gate jobs fail because ansible is not installed properly

e-r query: https://review.openstack.org/#/c/224893/

This only hits on OVH now:

http://logstash.openstack.org/#dashboard/file/logstash.json?query=message%3A%5C%22%2Ftmp%2Fansible%2Fbin%2Fansible%3A%20No%20such%20file%20or%20directory%5C%22%20AND%20tags%3A%5C%22console%5C%22%20AND%20voting%3A1&from=7d

I also seem to have similar issues on py3 unit tests jobs (was running on rax?)

http://logs.openstack.org/24/469624/2/check/gate-ironic-python35/9a19d98/console.html#_2017-06-01_06_46_58_000808

it seems there's some failure due to six is not available in the environment when setuptools tries to use it, which is also present in the logs of jobs described above (ansible was not installed due to the same failure - http://logs.openstack.org/24/469624/2/check/gate-tempest-dsvm-ironic-pxe_ipmitool-postgres-ubuntu-xenial-nv/ba57cc8/console.html#_2017-06-01_06_45_13_483721

and a new release of setuptools 36 was just pushed today (June 1, 2017). coincidence? :)

I also see such error in logs

Complete output from command python setup.py egg_info:
  Traceback (most recent call last):
    File "/home/jenkins/workspace/gate-ironic-python35/.tox/py35/lib/python3.5/site-packages/setuptools/dist.py", line 418, in fetch_build_egg
      cmd = self._egg_fetcher
  AttributeError: 'Distribution' object has no attribute '_egg_fetcher'

http://logs.openstack.org/24/469624/2/check/gate-ironic-python35/9a19d98/console.html#_2017-06-01_06_46_58_647784

oops, this is a very old bug...

see the following for the issue we're suffering from right now.
https://bugs.launchpad.net/devstack/+bug/1694904
https://github.com/pypa/setuptools/issues/1042

Updated the title to specifically mention devstack-gate as it is the tool relying on ansible being installed properly. Also, remove specific mention of the cloud involved as this issue can happen on any cloud when setuptools is not working. Hopefully this makes the general issue and how to tackle it more clear.