Use upper-constraints for all requirements when testing

When running unit tests the dependencies listed in requirements.txt has
to be explicitly installed with upper constraints as well, otherwise
they will be installed later without any constraints causing errors in
case of dependency issues.

Change-Id: I979a7d2b5cbeac1f191e5fc08ffe99df6301daab

tox.ini

@@ -9,6 +9,7 @@ allowlist_externals =
 deps =
   -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
   -r{toxinidir}/test-requirements.txt
+  -r{toxinidir}/requirements.txt
 passenv = OSLO_LOG_TEST_EVENTLET
 commands =
   find . -type f -name "*.pyc" -delete