Just look at the existing proxied remotes that correspond to already
existing nodes of the cluster, and keep those nodes in the cluster.
While adding any remotes of the local repo that are configured as
cluster nodes. This allows removing cluster nodes from the local repo
and updating, without it also removing nodes provided by other gateways.
One benefit of this is that a typo in annex-cluster-node config won't
init a new cluster.
Also it gets the cluster description set and is consistent with
initremote.
