HDFS-7869. Update action param from 'start' to 'prepare' in rolling upgrade ( Contributed by J.Andreina)

(cherry picked from commit 338b477ff7)

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -17,6 +17,9 @@ Release 2.8.0 - UNRELEASED
     HDFS-5356. MiniDFSCluster should close all open FileSystems when shutdown()
     (Rakesh R via vinayakumarb)
 
+    HDFS-7869. Update action param from "start" to "prepare" in rolling upgrade
+    javadoc (J.Andreina via vinayakumarb)
+
 Release 2.7.0 - UNRELEASED
 
   INCOMPATIBLE CHANGES

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DistributedFileSystem.java

@@ -1270,7 +1270,7 @@ public class DistributedFileSystem extends FileSystem {
   }
 
   /**
-   * Rolling upgrade: start/finalize/query.
+   * Rolling upgrade: prepare/finalize/query.
    */
   public RollingUpgradeInfo rollingUpgrade(RollingUpgradeAction action)
       throws IOException {

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

@@ -847,7 +847,7 @@ public interface ClientProtocol {
 
   /**
    * Rolling upgrade operations.
-   * @param action either query, start or finailze.
+   * @param action either query, prepare or finalize.
    * @return rolling upgrade information.
    */
   @Idempotent