With CoreDNS now supporting etcdv3 as the DNS backend, we
can update our federation target to etcdv3. Users will now be
able to use etcdv3 server as the federation backbone.
Minio will update bucket data to etcdv3 and CoreDNS can pick
that data up and serve it as bucket style DNS path.
This PR adds CopyObject support for objects residing in buckets
in different Minio instances (where Minio instances are part of
a federated setup).
Also, added support for multiple Minio domain IPs. This is required
for distributed deployments, where one deployment may have multiple
nodes, each with a different public IP.