filer prefer volume server in same data center (#3405)

* initial prefer same data center
https://github.com/seaweedfs/seaweedfs/issues/3404

* GetDataCenter

* prefer same data center for ReplicationSource

* GetDataCenterId

* remove glog

weed/topology/topology_info.go

@@ -76,8 +76,9 @@ func (t *Topology) ToVolumeLocations() (volumeLocations []*master_pb.VolumeLocat
 			for _, d := range rack.Children() {
 				dn := d.(*DataNode)
 				volumeLocation := &master_pb.VolumeLocation{
-					Url:       dn.Url(),
-					PublicUrl: dn.PublicUrl,
+					Url:        dn.Url(),
+					PublicUrl:  dn.PublicUrl,
+					DataCenter: dn.GetDataCenterId(),
 				}
 				for _, v := range dn.GetVolumes() {
 					volumeLocation.NewVids = append(volumeLocation.NewVids, uint32(v.Id))