follow the redirected master

fix https://github.com/chrislusf/seaweedfs/issues/1070

weed/wdclient/masterclient.go

@@ -79,10 +79,8 @@ func (mc *MasterClient) tryConnectToMaster(master string) (nextHintedLeader stri
 			return err
 		}
 
-		if mc.currentMaster == "" {
 		glog.V(1).Infof("%s Connected to %v", mc.name, master)
 		mc.currentMaster = master
-		}
 
 		for {
 			volumeLocation, err := stream.Recv()