Comment 4 for bug 1669425

I've restarted maas-regiond and maas-rackd and noticed:

==> regiond.log <==
2017-03-02 10:19:05 maasserver: [error] ################################ Exception: 'JSONDecodeError' object has no attribute 'message' ################################
2017-03-02 10:19:05 maasserver: [error] Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/metadataserver/builtin_scripts/hooks.py", line 306, in update_node_physical_block_devices
    blockdevs = json.loads(output.decode("ascii"))
  File "/usr/lib/python3.5/json/__init__.py", line 319, in loads
    return _default_decoder.decode(s)
  File "/usr/lib/python3.5/json/decoder.py", line 339, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/usr/lib/python3.5/json/decoder.py", line 357, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

During handling of the above exception, another exception occurred:

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 177, 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 59, 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 190, in __call__
    result = self.error_handler(e, request, meth, em_format)
  File "/usr/lib/python3/dist-packages/piston3/resource.py", line 188, in __call__
    result = meth(request, *args, **kwargs)
  File "/usr/lib/python3/dist-packages/maasserver/api/support.py", line 298, in dispatch
    return function(self, request, *args, **kwargs)
  File "/usr/lib/python3/dist-packages/metadataserver/api.py", line 587, in signal
    target_status = process(node, request, status)
  File "/usr/lib/python3/dist-packages/metadataserver/api.py", line 450, in _process_commissioning
    node, node.current_commissioning_script_set, request, status)
  File "/usr/lib/python3/dist-packages/metadataserver/api.py", line 415, in _store_results
    script_result.store_result(**args)
  File "/usr/lib/python3/dist-packages/metadataserver/models/scriptresult.py", line 153, in store_result
    exit_status=self.exit_status)
  File "/usr/lib/python3/dist-packages/metadataserver/builtin_scripts/hooks.py", line 308, in update_node_physical_block_devices
    raise ValueError(e.message + ': ' + output)
AttributeError: 'JSONDecodeError' object has no attribute 'message'