Update TOX_CONSTRAINTS_FILE for stable/victoria

Update the URL to the upper-constraints file to point to the redirect
rule on releases.openstack.org so that anyone working on this branch
will switch to the correct upper-constraints list automatically when
the requirements repository branches.

Until the requirements repository has as stable/victoria branch, tests will
continue to use the upper-constraints list on master.

Change-Id: I1a6080d05d725f3fa4ad0f65f6c121b6f1caf112

tox.ini

@@ -11,7 +11,7 @@ ignore_basepython_conflict=true
 basepython = python3
 usedevelop = True
 deps =
-       -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+       -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/victoria}
        -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
 install_command = pip install {opts} {packages}