Modify the url of upper_constraints_file

Depends-On: http://lists.openstack.org/pipermail/openstack-discuss/2019-May/006478.html

Change-Id: I6442a6423d3ab4df5dc699ad594eb2244e9ef994

Author: pengyuesheng

tox.ini

@@ -5,7 +5,7 @@ skipsdist = True
 
 [testenv]
 usedevelop = True
-install_command = pip install -c{env:UPPER_CONSTRAINTS_FILE:https://opendev.org/openstack/requirements/raw/branch/master/upper-constraints.txt} -U {opts} {packages}
+install_command = pip install -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master} -U {opts} {packages}
 setenv =
    VIRTUAL_ENV={envdir}
 deps = -r{toxinidir}/requirements.txt