Update the constraints url
Update the constraints url

For more detail, please refer:
http://lists.openstack.org/pipermail/openstack-discuss/2019-May/006478.html

Change-Id: I5af911e4467f2dff329cee5b8954ddbb024a7373

ChameleonCloud/blazar,openstack/blazar,ChameleonCloud/blazar,stackforge/blazar,openstack/blazar,stackforge/blazar