remove py27 from tox.ini
remove py27 from tox.ini

Remove python 2 from envlist parameter. Check the link:

https://etherpad.openstack.org/p/drop-python2-support
https://governance.openstack.org/tc/goals/selected/ussuri/drop-py27.html

The plan is drop the python 2 support from OpenStack in Ussuri release.
Move the basepython parameter.

Change-Id: I74a8f60de9121eac8057bf083be55d4316609719

openstack/tripleo-common,openstack/tripleo-common