provide human friendly error msg for local port forwarding errors

[eyberg]

"qemu-system-x86_64: Could not set up host forwarding rule 'tcp::8080:8080'"

we should explicitly tell the user that there is probably something listening on this port already if un-privileged - I would almost go as far as to say we should show which process is listening on it

[arknable]

@eyberg how to reproduce this ?

[eyberg]

without running a tap - try running this example https://ops.city/ on the same port twice - you should get this error message complaining that qemu can't listen on the same port since something else is already listening on it - what we'd like is a more developer friendly message - "something is already listening on this port" - we could even go further and show the user what process id it is

[arknable]

This is what I output from port checking:

Port 8083 is being used by other application (PID 725270)

currently the checking is using lsof -i that should be available for linux and osx. will add windows support after I installed windows.

[fabioDMFerreira]

Currently, ops isn't supporting windows. Alternatively, windows users can use ops in WSL.

[arknable]

ah ok, will leave windows for now.