Update federation target to etcd/clientv3 (#6119)

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.

vendor/go.uber.org/multierr/README.md

@@ -0,0 +1,23 @@
+# multierr [![GoDoc][doc-img]][doc] [![Build Status][ci-img]][ci] [![Coverage Status][cov-img]][cov]
+
+`multierr` allows combining one or more Go `error`s together.
+
+## Installation
+
+    go get -u go.uber.org/multierr
+
+## Status
+
+Stable: No breaking changes will be made before 2.0.
+
+-------------------------------------------------------------------------------
+
+Released under the [MIT License].
+
+[MIT License]: LICENSE.txt
+[doc-img]: https://godoc.org/go.uber.org/multierr?status.svg
+[doc]: https://godoc.org/go.uber.org/multierr
+[ci-img]: https://travis-ci.org/uber-go/multierr.svg?branch=master
+[cov-img]: https://codecov.io/gh/uber-go/multierr/branch/master/graph/badge.svg
+[ci]: https://travis-ci.org/uber-go/multierr
+[cov]: https://codecov.io/gh/uber-go/multierr