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

other/java/client/src/main/proto/filer.proto

@@ -271,6 +271,7 @@ message Location {
     string url = 1;
     string public_url = 2;
     uint32 grpc_port = 3;
+    string data_center = 4;
 }
 message LookupVolumeResponse {
     map<string, Locations> locations_map = 1;