Use upper constraints for all jobs in tox.ini
Use upper constraints for all jobs in tox.ini

Openstack infra now supports upper constraints for
all jobs. Updated tox.ini to use upper constraints
for all jobs.

Change-Id: Id6080cf39ff5c50bc85b576247822040ccaae445
Closes-Bug: #1614361

StackStorm/mistral,StackStorm/mistral,openstack/mistral,openstack/mistral