It is very very strange that _setup returns a port
which is passed to _cleanup...
This is the only information the _cleanup helper needs and that is why
it survived the refactoring so far.
I think that _cleanup should simply remove all
ports, and that setup should not return a port
to begin with.
This assumes that blktests is the single user and can blindly remove
everything. I would like to play nice here and only cleanup resources
blktests actually allocates.
If someone needs the actual port number, then it
should either not use this _setup helper or
query it somehow.
I try to figure out how to implement such a query helper then.