HDFS-9947. Block#toString should not output information from derived classes (cmccabe)

(cherry picked from commit 9a43094e12ab8d35d49ceda2e2c5f83093bb3a5b)

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/protocol/Block.java

@@ -162,7 +162,9 @@ public class Block implements Writable, Comparable<Block> {
    */
   public static String toString(final Block b) {
     StringBuilder sb = new StringBuilder();
-    b.appendStringTo(sb);
+    sb.append(BLOCK_FILE_PREFIX).
+       append(b.blockId).append("_").
+       append(b.generationStamp);
     return sb.toString();
   }