add attribute timestamp in diagnosis

hdbtdbmonitor/src/main/java/org/tango/archiving/monitoring/database/MonitoringAgent.java

@@ -106,15 +106,19 @@ public class MonitoringAgent {
     private static void checkAttribute(final String attributeName, final AttributeInsertionReport report) {
         try {
             TangoAttribute att = new TangoAttribute(attributeName);
-            report.setTangoMessage("Attribute connection OK");
+            String tangoMessage = "Attribute connection OK";
+
             if (att.isScalar() && att.isNumber()) {
                 final String readValue = att.extract(String.class);
                 if (readValue.equalsIgnoreCase(Double.toString(Double.NaN))) {
-                    report.setTangoMessage("Attribute value is NaN");
+                    tangoMessage = "Attribute value is NaN";
                 }
             } else {
                 att.extract();
             }
+            final long lastTimeStamp = att.getTimestamp();
+            tangoMessage += ", read timestamp is " + (System.currentTimeMillis() - lastTimeStamp) + " ms ago";
+            report.setTangoMessage(tangoMessage);
             // TODO check if type of format has changed
 
             // Get current error message from archiver