HADOOP-10809. SyncableDataOutputStream must implement sync method on branch-2.

hadoop-tools/hadoop-azure/src/main/java/org/apache/hadoop/fs/azure/SyncableDataOutputStream.java

@@ -36,6 +36,12 @@ public class SyncableDataOutputStream extends DataOutputStream implements Syncab
     super(out);
   }
 
+  @Override
+  @Deprecated
+  public void sync() throws IOException {
+    hflush();
+  }
+
   @Override
   public void hflush() throws IOException {
     if (out instanceof Syncable) {