Clean up the tox.ini file

DHC-831
* remove unused environment variable
* remove old dependencies

Change-Id: If4326b533973c76402734fb33fed69dc20a8ab6c
Add openstack.nose_plugin to travis.yml and tox.ini

Change-Id: I60c4a87a490312f9761225eb4a41c0b31efa0372
Merge pull request #1 from rodis/master

Clean up the tox and travis configuration