HDFS-12215. DataNode.transferBlock does not create its daemon in the xceiver thread group. (Lei Xu)

Conflicts:
	hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DataNode.java

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DataNode.java

@@ -2919,7 +2919,8 @@ public class DataNode extends ReconfigurableBase
     b.setNumBytes(visible);
 
     if (targets.length > 0) {
-      new DataTransfer(targets, targetStorageTypes, b, stage, client).run();
+      new Daemon(new DataTransfer(targets, targetStorageTypes,
+          b, stage, client)).start();
     }
   }