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.

cmd/utils.go

@@ -142,6 +142,10 @@ const (
 	// Maximum Part ID for multipart upload is 10000
 	// (Acceptable values range from 1 to 10000 inclusive)
 	globalMaxPartID = 10000
+
+	// Default values used while communicating with the cloud backends
+	defaultDialTimeout   = 30 * time.Second
+	defaultDialKeepAlive = 30 * time.Second
 )
 
 // isMaxObjectSize - verify if max object size
@@ -263,8 +267,8 @@ func NewCustomHTTPTransport() *http.Transport {
 	return &http.Transport{
 		Proxy: http.ProxyFromEnvironment,
 		DialContext: (&net.Dialer{
-			Timeout:   30 * time.Second,
-			KeepAlive: 30 * time.Second,
+			Timeout:   defaultDialTimeout,
+			KeepAlive: defaultDialKeepAlive,
 		}).DialContext,
 		MaxIdleConns:          1024,
 		MaxIdleConnsPerHost:   1024,