Update TOX_CONSTRAINTS_FILE for stable/yoga

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

Change-Id: Ibda7417a79ce1c4aae5d5919c47a8bae48ce5dc5

Author: openstackadmin

tox.ini

@@ -15,7 +15,7 @@ setenv =
    PYTHONWARNINGS=default::DeprecationWarning
    OS_STDOUT_CAPTURE=1
    OS_STDERR_CAPTURE=1
-deps = -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+deps = -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/yoga}
        -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
 passenv = TEMPEST_* OS_TEST_*
@@ -108,7 +108,7 @@ commands = {toxinidir}/tools/cover.sh {posargs}
 
 [testenv:docs]
 deps =
-  -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+  -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/yoga}
   -r{toxinidir}/doc/requirements.txt
 commands =
   rm -rf doc/build/html doc/build/doctrees