HADOOP-16344. Make DurationInfo public unstable.

Contributed by Huan-Ping Su

Change-Id: I64a94cf382f9db78b4ef49a3912f25f0d906af7c

Author: pingsutw

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/DurationInfo.java

@@ -29,8 +29,8 @@
  * This allows it to be used in a try-with-resources clause, and have the
  * duration automatically logged.
  */
-@InterfaceAudience.Private
-@InterfaceStability.Unstable
+@Public
+@Unstable
 public class DurationInfo extends OperationDuration
     implements AutoCloseable {
   private final String text;