Use upper-constraints file when running tests

Currently, u-c is not uses so we are not using the versions specified in
requirements project.

Change-Id: Id0fd9e98103ff804a43f2d4485f72ac48df261c8

tox.ini

@@ -9,9 +9,11 @@ setenv = VIRTUAL_ENV={envdir}
          LANG=en_US.UTF-8
          LANGUAGE=en_US:en
          LC_ALL=C
+deps =
+  -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+  -r{toxinidir}/test-requirements.txt
+  -r{toxinidir}/requirements.txt
 
-deps = -r{toxinidir}/requirements.txt
-       -r{toxinidir}/test-requirements.txt
 commands = /usr/bin/find . -type f -name "*.pyc" -delete
            stestr run {posargs}