Update TOX_CONSTRAINTS_FILE for stable/zed

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/zed branch, tests will
continue to use the upper-constraints list on master.

Change-Id: If637dc6ab39d98f6bf7475349f1adc6fa28d45a6

tox.ini

@@ -8,7 +8,7 @@ basepython = python3
 usedevelop = True
 install_command = pip install {opts} {packages}
 deps =
-    -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+    -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/zed}
     -r{toxinidir}/requirements.txt
     -r{toxinidir}/test-requirements.txt
 commands = stestr run --slowest {posargs}
@@ -25,6 +25,6 @@ exclude = .venv,.tox,dist,*.egg,build,releasenotes
 show-source = true
 
 [testenv:releasenotes]
-deps = -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+deps = -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/zed}
        -r{toxinidir}/doc/requirements.txt
 commands = bash -c tools/releasenotes_tox.sh