upgrading from django 1.9 to 1.11 broke crossbar guest worker

After upgrading from django 1.9.6 to 1.11.11, running crossbar 17.10.1 with the following guest worker configuration fails due to not finding the DJANGO_SETTINGS_MODULE ("simpl_calc_model.settings").

{
    "type": "guest",
    "executable": "django-admin",
    "arguments": ["run_guest"],
    "options": {
        "workdir": "..",
        "env": {
            "vars": {
                "HOSTNAME": "localhost",
                "PORT": "8080"
            }
        }
    }
}

I'm running crossbar against this config from a management command in the project containing the simpl_calc_model directory. I can run the guest worker directly in this project like so:

./manage.py run_guest --settings=simpl_calc_model.settings

How to I ensure django-admin 1.11.11 can find the settings module when called from crossbar via my management command?

The error log looks like:

Traceback (most recent call last):
File " ~/.virtualenvs/simpl-calc-model/bin/django-admin", line 11, in <module>
sys.exit(execute_from_command_line())
File " ~/.virtualenvs/simpl-calc-model/lib/python3.6/site-packages/django/core/management/__init__.py", line 364, in execute_from_command_line
utility.execute()
File " ~/.virtualenvs/simpl-calc-model/lib/python3.6/site-packages/django/core/management/__init__.py", line 308, in execute
settings.INSTALLED_APPS
File " ~/.virtualenvs/simpl-calc-model/lib/python3.6/site-packages/django/conf/__init__.py", line 56, in __getattr__
self._setup(name)
File " ~/.virtualenvs/simpl-calc-model/lib/python3.6/site-packages/django/conf/__init__.py", line 41, in _setup
self._wrapped = Settings(settings_module)
File " ~/.virtualenvs/simpl-calc-model/lib/python3.6/site-packages/django/conf/__init__.py", line 110, in __init__
mod = importlib.import_module(self.SETTINGS_MODULE)
File " ~/.virtualenvs/simpl-calc-model/lib/python3.6/importlib/__init__.py", line 126, in import_module
return _bootstrap._gcd_import(name[level:], package, level)
File "<frozen importlib._bootstrap>", line 994, in _gcd_import
File "<frozen importlib._bootstrap>", line 971, in _find_and_load
File "<frozen importlib._bootstrap>", line 941, in _find_and_load_unlocked
File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
File "<frozen importlib._bootstrap>", line 994, in _gcd_import
File "<frozen importlib._bootstrap>", line 971, in _find_and_load
File "<frozen importlib._bootstrap>", line 953, in _find_and_load_unlocked
ModuleNotFoundError: No module named 'simpl_calc_model'  

Fixed problem by implementing Alasdair's suggestion and removing workdir:

{
    "type": "guest",
    "executable": "manage.py",
    "arguments": ["run_guest"],
    "options": {
        "env": {
            "vars": {
                "HOSTNAME": "localhost",
                "PORT": "8080"
            }
        }
    }
}