HDFS-8486. Addendum patch to fix backporting bug.

(cherry picked from commit 6c9e26609ceac5d16434cc7f4a1013e6faacd92f)

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

@@ -1282,7 +1282,7 @@ public class DataNode extends ReconfigurableBase
     checkDiskError();
 
     data.addBlockPool(nsInfo.getBlockPoolID(), conf);
-    initDirectoryScanner(conf);
+    initPeriodicScanners(conf);
   }
 
   BPOfferService[] getAllBpOs() {