Fix a build break in HDFS-1312

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/diskbalancer/DiskBalancerException.java

@@ -33,7 +33,9 @@ public class DiskBalancerException extends IOException {
     PLAN_ALREADY_IN_PROGRESS,
     INVALID_VOLUME,
     INVALID_MOVE,
-    INTERNAL_ERROR
+    INTERNAL_ERROR,
+    NO_SUCH_PLAN,
+    UNKNOWN_KEY
   }
 
   private final Result result;