Error on first run of ./dev sampledata

[courtneycb]

This seems to have been introduced in #83

On the first run of sampledata after a fresh build/start/update the error pasted at the bottom of this issue occurs.

This happens when we try to create a batch of question attempts (error in AttemptFactory.py). so far I am unsure what the exact issue is. But as this is only a local error and the sampledata command runs fine on a second run this is low priority.

Research studies loaded.
Traceback (most recent call last):
  File "./manage.py", line 27, in <module>
    execute_from_command_line(sys.argv)
  File "/docker_venv/lib/python3.6/site-packages/django/core/management/__init__.py", line 381, in execute_from_command_line
    utility.execute()
  File "/docker_venv/lib/python3.6/site-packages/django/core/management/__init__.py", line 375, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/docker_venv/lib/python3.6/site-packages/django/core/management/base.py", line 316, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/docker_venv/lib/python3.6/site-packages/django/core/management/base.py", line 353, in execute
    output = self.handle(*args, **options)
  File "/codewof/codewof/general/management/commands/sampledata.py", line 83, in handle
    AttemptFactory.create_batch(size=50)
  File "/docker_venv/lib/python3.6/site-packages/factory/base.py", line 576, in create_batch
    return [cls.create(**kwargs) for _ in range(size)]
  File "/docker_venv/lib/python3.6/site-packages/factory/base.py", line 576, in <listcomp>
    return [cls.create(**kwargs) for _ in range(size)]
  File "/docker_venv/lib/python3.6/site-packages/factory/base.py", line 564, in create
    return cls._generate(enums.CREATE_STRATEGY, kwargs)
  File "/docker_venv/lib/python3.6/site-packages/factory/django.py", line 141, in _generate
    return super(DjangoModelFactory, cls)._generate(strategy, params)
  File "/docker_venv/lib/python3.6/site-packages/factory/base.py", line 501, in _generate
    return step.build()
  File "/docker_venv/lib/python3.6/site-packages/factory/builder.py", line 272, in build
    step.resolve(pre)
  File "/docker_venv/lib/python3.6/site-packages/factory/builder.py", line 221, in resolve
    self.attributes[field_name] = getattr(self.stub, field_name)
  File "/docker_venv/lib/python3.6/site-packages/factory/builder.py", line 375, in __getattr__
    extra=context,
  File "/docker_venv/lib/python3.6/site-packages/factory/declarations.py", line 196, in evaluate
    value = next(iter(self.iterator))
StopIteration```