sandbox/io: default interpreter path when using uwsgi

For whatever reason, uwsgi modifies 'sys.executable' when running, which causes the io Server to be called with uwsgi, and not the python interpreter.

Defaulting the interpreter to the one used in the Docker production container, if uwsgi is in the executable path. Hardcoding is not preferred, but considering this is setup to be executed in a Docker container, the path can be kept consistent across all users.

Not particularly an ideal solution, but I can't think of another way to determine the right interpreter without sys.executable.