always fire LOCAL_IPS.extend(PUBLIC_IPS)

was in `else`, but should have been `finally` so it aways runs.


Symptom was warnings in parallel.client about `127.0.1.1` not being this machine.
Use Instance trait for user_ns instead of Dict.

Instance(dict) is None by default, unlike Dict().
Add a test for kernel started without user_ns kwarg.

user_module should not be an instance of DummyMod