init rack can't find secrets

[Huw Wilkins]

The edge snap fails to add a controller with a secrets file error.

I installed MAAS in an LXC container with:

snap install maas --channel=latest/edge

Then tried:

sudo maas init rack --maas-url ... --secret ...

Which gave the following error:

Traceback (most recent call last):
  File "/snap/maas/21248/bin/maas", line 8, in <module>
    sys.exit(main())
  File "/snap/maas/21248/lib/python3.8/site-packages/maascli/__init__.py", line 39, in main
    options.execute(options)
  File "/snap/maas/21248/lib/python3.8/site-packages/maascli/snap.py", line 448, in __call__
    raise exc
  File "/snap/maas/21248/lib/python3.8/site-packages/maascli/snap.py", line 445, in __call__
    self.handle(options)
  File "/snap/maas/21248/lib/python3.8/site-packages/maascli/snap.py", line 646, in handle
    set_rpc_secret(rpc_secret)
  File "/snap/maas/21248/lib/python3.8/site-packages/maascli/snap.py", line 262, in set_rpc_secret
    secret_path.write_text(secret)
  File "/usr/lib/python3.8/pathlib.py", line 1255, in write_text
    with self.open(mode='w', encoding=encoding, errors=errors) as f:
  File "/usr/lib/python3.8/pathlib.py", line 1222, in open
    return io.open(self, mode, buffering, encoding, errors, newline,
  File "/usr/lib/python3.8/pathlib.py", line 1078, in _opener
    return self._accessor.open(self, flags, mode)
FileNotFoundError: [Errno 2] No such file or directory: '/var/snap/maas/common/maas/secret'

I also tried in a fresh lxc container using the 3.1 snap and it worked fine.

This looks like the same error that was resolved in 2.8: https://bugs.launchpad.net/maas/+bug/1885005