Description of problem:

Running neutron tests for RHOSP 10/newton fails with the following error:

Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/fixtures/fixture.py", line 212, in setUp
    raise MultipleExceptions(*errors)
testtools.runtest.MultipleExceptions: ((<class 'oslo_config.cfg.ConfigFilesPermissionDeniedError'>, ConfigFilesPermissionDeniedError(), <traceback object at 0x5ba7830>), (<class 'fixtures.fixture.SetupError'>, SetupError({},), <traceback object at 0x5ba7950>))

It happens because we have old version of python-fixtures (v1) and according to 
global requirements (and neutron requirements) we need at least >= 3 version.

https://github.com/openstack/requirements/blob/master/global-requirements.txt#L318


How reproducible: 100%


Steps to Reproduce:
1. Clone neutron OSP 10/newton
2. Run tox -e dsvm-functional

Actual results: Failure


Expected results: Tests passed successfully