Update UPPER_CONSTRAINTS_FILE for stable/pike

Change-Id: I20e15b33e36bb3c9f1b60e2bf5fee36470c46878

tox.ini

@@ -7,7 +7,7 @@ setenv =
     VIRTUAL_ENV={envdir}
     BRANCH_NAME=master
     CLIENT_NAME=oslo.versionedobjects
-install_command = {toxinidir}/tools/tox_install.sh {env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt} {opts} {packages}
+install_command = {toxinidir}/tools/tox_install.sh {env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt?h=stable/pike} {opts} {packages}
 deps = .[fixtures]
        -r{toxinidir}/test-requirements.txt
 commands = python setup.py testr --slowest --testr-args='{posargs}'