ClosNetwork: refine some logging
ClosNetwork: remove unused key
ClosNetwork: fix two disconnection bugs

A switch that disconnected and then connected back had role of all ports
stuck to "none". Moving @port_role initialization from CNSwitch.reset()
to CNSwitch.initialize() fixes this.

A leaf switch did not feed "withdraw" tasks back to the topology when it
was disconnected. Overloading forgetDestination() to generate the tasks
in CNLeafSwitch only and always proxying its returned value to the
topology fixes this.