Use upper-constraints for all tox targets
Use upper-constraints for all tox targets

The issue has been resolved by infra [0], so we can use upper
constraints for all targets.

[0]
http://lists.openstack.org/pipermail/openstack-dev/2016-August/101474.html

Change-Id: I72e5139a23a01e6d374c8fc9187903b0f2cb8118

openstack/python-dracclient