Bring etcd support for bucket DNS federation

- Supports centralized `config.json`
- Supports centralized `bucket` service records
  for client lookups
- implement a new proxy forwarder

vendor/github.com/ugorji/go/codec/gen_16.go

@@ -0,0 +1,12 @@
+// Copyright (c) 2012-2015 Ugorji Nwoke. All rights reserved.
+// Use of this source code is governed by a MIT license found in the LICENSE file.
+
+// +build go1.6
+
+package codec
+
+import "os"
+
+func init() {
+	genCheckVendor = os.Getenv("GO15VENDOREXPERIMENT") != "0"
+}