Update TOX_CONSTRAINTS_FILE
Update 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>.

Change-Id: I9fd924030a0a5dd4852fa8cfd0ca807038090304

openstack/python-senlinclient,openstack/python-senlinclient