Comment 0 for bug 1746558

Currently the "get_minimum_version_all_cells" functions in service runs sequentially and this affects the performance in case of large deployments (running a lot of cells) : https://github.com/openstack/nova/blob/stable/pike/nova/objects/service.py#L440

So it would be nice to use the scatter_gather_all_cells function to do this operation in parallel.