tox command doesn't work anymore to run neutron tests

[Mathieu Rohon]

using tox 2.3.0 with the tox.ini from neutron leads to this kind of error:

$ tox -e pep8
Traceback (most recent call last):
  File "/usr/local/bin/tox", line 11, in <module>
    sys.exit(cmdline())
  File "/usr/local/lib/python2.7/dist-packages/tox/session.py", line 38, in main
    config = prepare(args)
  File "/usr/local/lib/python2.7/dist-packages/tox/session.py", line 26, in prepare
    config = parseconfig(args)
  File "/usr/local/lib/python2.7/dist-packages/tox/config.py", line 229, in parseconfig
    parseini(config, inipath)
  File "/usr/local/lib/python2.7/dist-packages/tox/config.py", line 729, in __init__
    self.make_envconfig(name, section, reader._subs, config)
  File "/usr/local/lib/python2.7/dist-packages/tox/config.py", line 760, in make_envconfig
    res = meth(env_attr.name, env_attr.default)
  File "/usr/local/lib/python2.7/dist-packages/tox/config.py", line 893, in getdict_setenv
    definitions = self._getdict(value, default=default, sep=sep)
  File "/usr/local/lib/python2.7/dist-packages/tox/config.py", line 904, in _getdict
    name, rest = line.split('=', 1)
ValueError: need more than 1 value to unpack

The root cause seems to be a bug in tox 2.3.0 :
https://bitbucket.org/hpk42/tox/issues/181

It works fine with tox 2.3.1.

Other openstack projects report similar errors :

https://bugs.launchpad.net/devstack/+bug/1525352

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/269633

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/269633
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=3b2b277979f8d0335fcfcef29893290ef20cb9f7
Submitter: Jenkins
Branch: master

commit 3b2b277979f8d0335fcfcef29893290ef20cb9f7
Author: Mathieu Rohon <email address hidden>
Date: Tue Jan 19 13:28:24 2016 +0000

    bump the min tox version to 2.3.1

    When tox 2.3.0 uses the tox.ini provided by neutron,
    the following bug is hitten :
    https://bitbucket.org/hpk42/tox/issues/181
    We need to set the min version of tox to 2.3.1.

    Change-Id: If2c3f4f534ff23a1f649cebea15e945563173544
    Closes-bug: #1535725