Note: Currently it fails, maybe some work will be required.

It proves up to the end -- that communication with supervisord was done and
that service was correctly started.

Additionaly fix small issue with test assertions.

Mock netifaces in order to simulate real behaviour of machine. Add another
part of "persistence", which allows simulation of network stack.

Make test more flexible and controlallbe by exposing groups.

Additionally add required "persistence" to test.

Duplicate Listbox_asHTML from xhtml skin in vifib_hosting_theme, change checkbox buttons to radio buttons.

Possible this test detected another failing use case during destruction.
That's why it is still marked with NotImplementedError

It is already requirement for slapos.core, and it is well known code.

Ue multiprocessing instead of threading, as there is no other way to kill
Flask application from code except SIGTERMing it.