Comment 7 for bug 1606823

After resolving of https://bugs.launchpad.net/fuel/+bug/1622579 - the issue got back with new symptoms(snapshot 255):

 2016-09-13 14:42:05.839 ERROR [7fe3ce45a880] (manager) Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/nailgun/task/manager.py", line 61, in _call_silently
    to_return = method(task, *args, **kwargs)
  File "/usr/lib/python2.7/site-packages/nailgun/task/task.py", line 268, in message
    dry_run=dry_run, **kwargs
  File "/usr/lib/python2.7/site-packages/nailgun/task/task.py", line 146, in call_deployment_method
    args = getattr(cls, method)(transaction, **kwargs)
  File "/usr/lib/python2.7/site-packages/nailgun/task/task.py", line 382, in granular_deploy
    cls._extend_tasks_list(pre_deployment, pre_deployment_affected)
  File "/usr/lib/python2.7/site-packages/nailgun/task/task.py", line 320, in _extend_tasks_list
    t['uids'].extend(src_dict[t['id']]['uids'])
AttributeError: 'set' object has no attribute 'extend'