Since  devstack is failing on s390x with "Distro not supported".
The reason for this is the missing etcd3 support. It worked before
 as we were able to disable etcd3 via local.conf. But as etcd3 is
a base service, we might not be able to rely on this workarond in
the future anymore.
As there is no etcd3 binary hosted on github like it is for other
architectures, the user needs to specify an alternative download
URL via local.conf. Otherwise devstack will exit with an appropriate