Update tox.ini

* Move basepython to [testenv] which is a place to define common things
* Move upper-constraints from install_command to deps
* Update the min version to 2.0 to allow http links in deps
* Cleanup unused tox envs ('cover' and 'debug')
* Drop unnecessary envs from envlist (only pep8 is used now)

Change-Id: Ie915a93b824331407a48affcbd31076d6a7cccfa
1 file changed