Use TOX_CONSTRAINTS_FILE
Use TOX_CONSTRAINTS_FILE

UPPER_CONSTRAINTS_FILE is old name and deprecated
-https://zuul-ci.org/docs/zuul-jobs/python-roles.html#rolevar-tox.tox_constraints_file
This allows to use lower-constraints file as more
readable way instead of UPPER_CONSTRAINTS_FILE=<lower-constraints file>.

[1] https://review.opendev.org/#/c/722814/

Change-Id: I82d482bba3e4c40913583fb26f692824c56e6ac1

openstack/octavia,openstack/octavia,openstack/octavia