Comment 13 for bug 1781286

I think this is also for reschedules during server create because of this call:

https://github.com/openstack/nova/blob/4c37ff72e5446c835a48d569dd5a1416fcd36c71/nova/conductor/manager.py#L657

build_instances in the cell conductor won't be able to hit aggregates in the API DB if the cell conductor isn't configured for the API DB.