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/replication/sink/filersink/fetch_write.go

@@ -139,6 +139,11 @@ func (fs *FilerSink) WithFilerClient(streamingMode bool, fn func(filer_pb.Seawee
 	}, fs.grpcAddress, fs.grpcDialOption)
 
 }
+
 func (fs *FilerSink) AdjustedUrl(location *filer_pb.Location) string {
 	return location.Url
 }
+
+func (fs *FilerSink) GetDataCenter() string {
+	return fs.dataCenter
+}