QMP: Introduce basic asynchronous events

Debug, shutdown, reset, powerdown and stop are all basic events,
as they are very simple they can be added in the same commit.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

monitor.c

@@ -342,6 +342,21 @@ void monitor_protocol_event(MonitorEvent event, QObject *data)
         return;
 
     switch (event) {
+        case EVENT_DEBUG:
+            event_name = "DEBUG";
+            break;
+        case EVENT_SHUTDOWN:
+            event_name = "SHUTDOWN";
+            break;
+        case EVENT_RESET:
+            event_name = "RESET";
+            break;
+        case EVENT_POWERDOWN:
+            event_name = "POWERDOWN";
+            break;
+        case EVENT_STOP:
+            event_name = "STOP";
+            break;
         default:
             abort();
             break;