fix skywire-cli vpn subcommands

[0pcom]

start

the logging returned by skywire-cli vpn start command is not very helpful.

It should probably show (or have an option to show) the debug logging from the visor around the establishment of transports, and to actually return when the vpn client has started successfully or when it has stopped (as in failed to start).

The command should not return until either the vpn client has started successfully or an error is generated

list

skywire-cli vpn list is buggy and inconsistent. as though its not waiting long enough for the response to the request. if you keep executing it, eventually it will succeed but its very inconsistent

transport logic

the logic for transport creation should be checked again to make sure its working well. sometimes the vpn works better when a transport is created manually first.