Use TOX_CONSTRAINTS_FILE
Use TOX_CONSTRAINTS_FILE

UPPER_CONSTRAINTS_FILE is old name and deprecated.
This allows to use upper-constraints file as more
readable way instead of UPPER_CONSTRAINTS_FILE=<lower-constraints file>.
For more info. please refer [1].

[1] https://zuul-ci.org/docs/zuul-jobs/python-roles.html#rolevar-tox.tox_constraints_file

Change-Id: I5403b96d4dd0faac9f1295d57a1680a7d452c7b1

openstack/monasca-ui,openstack/monasca-ui,stackforge/monasca-ui,openstack/monasca-ui,openstack/monasca-ui,stackforge/monasca-ui,stackforge/monasca-ui,stackforge/monasca-ui