Detect celery workflow meta tasks with task.type instead of hasattr

This make code more readable and less error prone.

cubicweb_celerytask/entities.py

@@ -257,11 +257,11 @@ class CeleryTaskAdapter(ICeleryTask):
                                             task_name=task_name,
                                             parent_task=parent)
         seen.add(task_id)
-        if hasattr(task, 'body'):
-            self.attach_task(task.body, seen, parent)
-        if hasattr(task, 'tasks'):
+        if task.name in ('celery.chord', 'celery.chain', 'celery.group'):
             for subtask in task.tasks:
                 self.attach_task(subtask, seen, parent)
+        if task.name == 'celery.chord':
+            self.attach_task(task.body, seen, parent)
 
     def get_task(self, name, *args, **kwargs):
         task = super(CeleryTaskAdapter, self).get_task(