UPPER_CONSTRAINTS_FILE is deprecated and TOX_CONSTRAINTS_FILE is
the new environment variable name that replaces it [1].
This allows to use upper-constraints file as more
readable way instead of UPPER_CONSTRAINTS_FILE=<lower-constraints file>.
[1] https://zuul-ci.org/docs/zuul-jobs/python-roles.html#rolevar-tox.tox_constraints_file
[2] https://review.opendev.org/#/c/722814/
Change-Id: I668ab8cdfb3ec49bb26d890630c823419c8cb3de
[testenv]
basepython = python3
-install_command = pip install -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master} {opts} {packages}
+install_command = pip install -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master} {opts} {packages}
[testenv:releasenotes]
deps = -r{toxinidir}/doc/requirements.txt