Error while converting errors in uptests

[ghost]

Originally reported by: Anonymous

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The uptest task vr.server.tasks.uptest_host can fail in such a way that it returns, as a result, an Exception object.
VR then tries to convert the Exception object to YAML (using yaml.safe_dump) which fails with a RepresenterError error.
The root cause seems to be that not always failed calls of Fabric's sudo return a result with the attribute failed, which is what VR uses to decide how to handle the result (see Error class in remote.py).

Full stack trace below.

#!shell

Traceback (most recent call last):
  File "/app/.heroku/venv/lib/python2.7/site-packages/celery/app/trace.py", line 240, in trace_task
    R = retval = fun(*args, **kwargs)
  File "/app/.heroku/venv/lib/python2.7/site-packages/newrelic-2.68.0.50/newrelic/hooks/application_celery.py", line 84, in wrapper
    return wrapped(*args, **kwargs)
  File "/app/.heroku/venv/lib/python2.7/site-packages/celery/app/trace.py", line 438, in __protected_call__
    return self.run(*args, **kwargs)
  File "/app/.heroku/venv/lib/python2.7/site-packages/vr/server/tasks.py", line 740, in uptest_host
    results=yaml.safe_dump(resultlist)
  File "/app/.heroku/venv/lib/python2.7/site-packages/yaml/__init__.py", line 218, in safe_dump
    return dump_all([data], stream, Dumper=SafeDumper, **kwds)
  File "/app/.heroku/venv/lib/python2.7/site-packages/yaml/__init__.py", line 190, in dump_all
    dumper.represent(data)
  File "/app/.heroku/venv/lib/python2.7/site-packages/yaml/representer.py", line 28, in represent
    node = self.represent_data(data)
  File "/app/.heroku/venv/lib/python2.7/site-packages/yaml/representer.py", line 57, in represent_data
    node = self.yaml_representers[data_types[0]](self, data)
  File "/app/.heroku/venv/lib/python2.7/site-packages/yaml/representer.py", line 215, in represent_list
    return self.represent_sequence(u'tag:yaml.org,2002:seq', data)
  File "/app/.heroku/venv/lib/python2.7/site-packages/yaml/representer.py", line 101, in represent_sequence
    node_item = self.represent_data(item)
  File "/app/.heroku/venv/lib/python2.7/site-packages/yaml/representer.py", line 57, in represent_data
    node = self.yaml_representers[data_types[0]](self, data)
  File "/app/.heroku/venv/lib/python2.7/site-packages/yaml/representer.py", line 223, in represent_dict
    return self.represent_mapping(u'tag:yaml.org,2002:map', data)
  File "/app/.heroku/venv/lib/python2.7/site-packages/yaml/representer.py", line 123, in represent_mapping
    node_value = self.represent_data(item_value)
  File "/app/.heroku/venv/lib/python2.7/site-packages/yaml/representer.py", line 67, in represent_data
    node = self.yaml_representers[None](self, data)
  File "/app/.heroku/venv/lib/python2.7/site-packages/yaml/representer.py", line 247, in represent_undefined
    raise RepresenterError("cannot represent an object: %s" % data)
RepresenterError: cannot represent an object: sudo: unable to send audit message: Operation not permitted

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• Bitbucket: https://bitbucket.org/yougov/velociraptor/issue/206