Comment 2 for bug 1556185

saw this again. It may be causing some machines to fail enlist

2016-04-02 06:32:57 [-] 127.0.0.1 - - [01/Apr/2016:22:32:56 +0000] "POST /MAAS/api/2.0/machines/ HTTP/1.1" 500 32 "-" "curl/7.47.0"
2016-04-02 06:32:57 [-] /usr/lib/python3/dist-packages/piston3/authentication.py:314: django.utils.deprecation.RemovedInDjango19Warning: `request.REQUEST` is deprecated, use `request.GET` or `request.POST` instead.
2016-04-02 06:32:57 [-] /usr/lib/python3/dist-packages/django/core/handlers/wsgi.py:126: django.utils.deprecation.RemovedInDjango19Warning: `MergeDict` is deprecated, use `dict.update()` instead.
2016-04-02 06:32:57 [maasserver] ERROR: ################################ Exception: 'Machine' object is not iterable ################################
2016-04-02 06:32:57 [maasserver] ERROR: Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/django/core/handlers/base.py", line 132, in get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/usr/lib/python3/dist-packages/maasserver/utils/views.py", line 180, in view_atomic_with_post_commit_savepoint
    return view_atomic(*args, **kwargs)
  File "/usr/lib/python3.5/contextlib.py", line 30, in inner
    return func(*args, **kwds)
  File "/usr/lib/python3/dist-packages/maasserver/api/support.py", line 54, in __call__
    response = upcall(request, *args, **kwargs)
  File "/usr/lib/python3/dist-packages/django/views/decorators/vary.py", line 21, in inner_func
    response = func(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/piston3/resource.py", line 229, in __call__
    else: stream = srl.render(request)
  File "/usr/lib/python3/dist-packages/piston3/emitters.py", line 464, in render
    response = serializers.serialize(format, self.data, indent=True)
  File "/usr/lib/python3/dist-packages/django/core/serializers/__init__.py", line 129, in serialize
    s.serialize(queryset, **options)
  File "/usr/lib/python3/dist-packages/django/core/serializers/base.py", line 52, in serialize
    for obj in queryset:
TypeError: 'Machine' object is not iterable

2016-04-02 06:32:57 [-] 127.0.0.1 - - [01/Apr/2016:22:32:57 +0000] "POST /MAAS/api/2.0/machines/ HTTP/1.1" 500 32 "-" "curl/7.47.0"
2016-04-02 06:32:58 [-] Successfully configured DNS.
2016-04-02 06:32:58 [RegionServer,0,192.168.20.104] Successfully configured DHCPv4 on rack controller '4y3h7n'.
2016-04-02 06:32:58 [RegionServer,0,192.168.20.104] Successfully configured DHCPv4 on rack controller '4y3h7n'.
2016-04-02 06:32:58 [-] Successfully configured DNS.