Run functional tests against both Python 2 and 3

[Brian Curtin]

We currently only run functional tests in the current environment a developer has setup, which in the gate is always Python 2. I run my local virtualenvs as Python 3, and I see some failures that don't appear elsewhere. When I switch and run a Py2 environment, everything passes.

We should have two functional test targets, one per version.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/218392

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/218392
Committed: https://git.openstack.org/cgit/stackforge/python-openstacksdk/commit/?id=f956917c0d7ba5b623617332d632bfbef47c4482
Submitter: Jenkins
Branch: master

commit f956917c0d7ba5b623617332d632bfbef47c4482
Author: Brian Curtin <email address hidden>
Date: Fri Aug 28 12:12:46 2015 -0500

    Add tox targets for functional testing on 2 and 3

    Previously, the functional tests would run using the `python` in your
    environment, which was 3 for myself and 2 for most others. We should
    really be testing on both versions as we do for unit tests. A change to
    the gate will follow this.

    Change-Id: I2bd2664018c135593a96fd6ba5741279da772e76
    Closes-Bug: 1489935