add check if port 16600 is open when starting nelson

[gjeee]

all the while i thought i was running nelson correctly. now and then i saw for a short time a new dynamic node....so i thought everything was fine. however i became a bit suspicious after i checked my nelson logs and i always saw these new connections getting dropped almost instantaneously.

after a bit of research i finally realized i forgot to open port 16600. my suggestion would be therefore to add a check if port 16600 is open when one starts nelson and throw an error if port is firewalled.