Add notification for pause/unpause instance

When pause/unpause instance, there are no notifications, this
will cause someone cannot know when pause/unpause operation
would be finished.

All other instance operations do have notifications. We should
also add notification support for those two operations.

Change-Id: I5b8cc33a5992f5f028a3220217dcf7a0288d150d
Closes-Bug: #1043861

nova/compute/manager.py

@@ -3215,12 +3215,14 @@ def pause_instance(self, context, instance):
         """Pause an instance on this host."""
         context = context.elevated()
         LOG.audit(_('Pausing'), context=context, instance=instance)
+        self._notify_about_instance_usage(context, instance, 'pause.start')
         self.driver.pause(instance)
         current_power_state = self._get_power_state(context, instance)
         instance.power_state = current_power_state
         instance.vm_state = vm_states.PAUSED
         instance.task_state = None
         instance.save(expected_task_state=task_states.PAUSING)
+        self._notify_about_instance_usage(context, instance, 'pause.end')
 
     @object_compat
     @wrap_exception()
@@ -3231,12 +3233,14 @@ def unpause_instance(self, context, instance):
         """Unpause a paused instance on this host."""
         context = context.elevated()
         LOG.audit(_('Unpausing'), context=context, instance=instance)
+        self._notify_about_instance_usage(context, instance, 'unpause.start')
         self.driver.unpause(instance)
         current_power_state = self._get_power_state(context, instance)
         instance.power_state = current_power_state
         instance.vm_state = vm_states.ACTIVE
         instance.task_state = None
         instance.save(expected_task_state=task_states.UNPAUSING)
+        self._notify_about_instance_usage(context, instance, 'unpause.end')
 
     @wrap_exception()
     def host_power_action(self, context, host=None, action=None):

nova/tests/compute/test_compute.py

@@ -1845,10 +1845,26 @@ def test_pause(self):
         self.compute.run_instance(self.context, instance=instance)
         db.instance_update(self.context, instance['uuid'],
                            {"task_state": task_states.PAUSING})
+        fake_notifier.NOTIFICATIONS = []
         self.compute.pause_instance(self.context, instance=instance)
+        self.assertEqual(len(fake_notifier.NOTIFICATIONS), 2)
+        msg = fake_notifier.NOTIFICATIONS[0]
+        self.assertEqual(msg.event_type,
+                         'compute.instance.pause.start')
+        msg = fake_notifier.NOTIFICATIONS[1]
+        self.assertEqual(msg.event_type,
+                         'compute.instance.pause.end')
         db.instance_update(self.context, instance['uuid'],
                            {"task_state": task_states.UNPAUSING})
+        fake_notifier.NOTIFICATIONS = []
         self.compute.unpause_instance(self.context, instance=instance)
+        self.assertEqual(len(fake_notifier.NOTIFICATIONS), 2)
+        msg = fake_notifier.NOTIFICATIONS[0]
+        self.assertEqual(msg.event_type,
+                         'compute.instance.unpause.start')
+        msg = fake_notifier.NOTIFICATIONS[1]
+        self.assertEqual(msg.event_type,
+                         'compute.instance.unpause.end')
         self.compute.terminate_instance(self.context, instance=instance)
 
     def test_suspend(self):