8132209: DiagnosticCommandImpl.getNotificationInfo() may expose internal representation

Summary: DiagnosticCommandImpl.getNotificationInfo() may expose internal representation
Reviewed-by: skoivu, fparain, jbachorik

src/share/classes/sun/management/DiagnosticCommandImpl.java

@@ -312,7 +312,7 @@ class DiagnosticCommandImpl extends NotificationEmitterSupport
                                                    "Diagnostic Framework Notification");
             }
         }
-        return notifInfo;
+        return notifInfo.clone();
     }
 
     private static long seqNumber = 0;