Use upper-constraints.txt for sahara-tests testing
Use upper-constraints.txt for sahara-tests testing

It aligns with the general good practice in OpenStack and
it prevents unexpected breakages coming from new library releases
(as it happens currently with urllib3 1.24.)

Change-Id: I1ad04708c088fa1e05beaa0d1915bae5420ad3c3

openstack/sahara-scenario,openstack/sahara-tests,openstack/sahara-tests,openstack/sahara-scenario,openstack/sahara-tests,openstack/sahara-tests,openstack/sahara-scenario