HDFS-10335 Mover$Processor#chooseTarget() always chooses the first matching target storage group. Contributed by Mingliang Liu

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/mover/Mover.java

@@ -478,7 +478,9 @@ public class Mover {
         List<StorageType> targetTypes, Matcher matcher) {
       final NetworkTopology cluster = dispatcher.getCluster(); 
       for (StorageType t : targetTypes) {
-        for(StorageGroup target : storages.getTargetStorages(t)) {
+        final List<StorageGroup> targets = storages.getTargetStorages(t);
+        Collections.shuffle(targets);
+        for (StorageGroup target : targets) {
           if (matcher.match(cluster, source.getDatanodeInfo(),
               target.getDatanodeInfo())) {
             final PendingMove pm = source.addPendingMove(db, target);