Use constraints in tox.ini
Use constraints in tox.ini

As per email [1] from Andreas, we can add upper constraints on packages
used now.

[1] http://openstack.markmail.org/thread/a4l7tokbotwqvuoh

Change-Id: Iaaacbac9d931a9deb3cfb53afaa4d1c16e84508e

openstack/senlin,stackforge/senlin,stackforge/senlin,openstack/senlin,openstack/senlin