Make subunit2html.py python2.6 compatible.
Make subunit2html.py python2.6 compatible.

* modules/jenkins/files/slave_scripts/subunit2html.py: Swap out unittest
with testtools for python 2.6 compatibility. Remove argparse and
manually parse argv for python 2.6 compatibility.

Change-Id: If3a253439550b5394b9b7eac129d8ed66b7ba951
Reviewed-on: https://review.openstack.org/26785
Reviewed-by: lifeless <a2625afd9a2a1367fa2df61966453044ff840158@robertcollins.net>
Reviewed-by: Jeremy Stanley <98883b97e35b7bb1ac282bb863f2e9d917db0454@yuggoth.org>
Approved: Monty Taylor <37c07a49ee3d5191376d758eb1d8298b34456b8e@inaugust.com>
Reviewed-by: Monty Taylor <37c07a49ee3d5191376d758eb1d8298b34456b8e@inaugust.com>
Tested-by: Jenkins

open-switch/infra_puppet-jenkins,open-switch/infra_puppet-jenkins