HDFS-13635. Incorrect message when block is not found. Contributed by Gabor Bota.

(cherry picked from commit fef20a446f7bf9f29e0f0ee690987fb6fc78a031)

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

@@ -37,7 +37,7 @@ public class ReplicaNotFoundException extends IOException {
       "Cannot recover append/close to a replica that's not FINALIZED and not RBW"
           + " ";
   public final static String NON_EXISTENT_REPLICA =
-      "Cannot append to a non-existent replica ";
+      "Replica does not exist ";
   public final static String UNEXPECTED_GS_REPLICA =
       "Cannot append to a replica with unexpected generation stamp ";