Overrides in `os`

[insertinterestingnamehere]

Currently Python modules isolated in VECs can potentially see things that we don't intend by simply using the Python-level os module. We should extend our overrides to cover those interfaces. Off the top of my head I'm not sure if this should be done at the libparla_supervisor level or by patching in new functions into Python's os module at runtime when we set up our import override.