Use upper-constraints for tox envs
Use upper-constraints for tox envs

Pin tox environments to upper-constraints to avoid conflicts with
library releases.

Change-Id: I46ba7cf37c52612c87d4db5086efe1a8b7c9f4a5

stackforge/refstack,openstack/refstack,openstack/refstack,stackforge/refstack,stackforge/refstack,openstack/refstack,openstack/refstack,stackforge/refstack