update and fix tox for our needs

- install pip from debian package, insteads of easy_install
- fix tox version error, force to use 1.6.1
see also https://bugs.launchpad.net/openstack-ci/+bug/1274135
- use tox to create virtual environment .tox
- disable module vcsrepo, use git insteads

SMBCAP-5020