Currently Beaker does not support multiple OpenStack regions. This is a feature left back in the initial implementation of the Openstack integration. See more details in https://beaker-project.org/dev/proposals/dynamic-virtualization.html#associating-lab-controllers-with-openstack-regions
This is low priority for us right now, since we are not aware of any OpenStack environment having multiple regions which anyone wants to use with Beaker.
This seems to be not a requirement, because multiple OpenStack regions have not been deployed so far. If it comes up again, we'll either reopen or create a new bug.