Trying to start a port forward doesn't look like it is doing anything

[Nokel81]

1. If the pod backing a port forward is pending then attempting to start the port forward will always fail, so maybe not allow it in the first place
2. When starting or stopping a port forward a spinner or change of status would be good to show that something is being done.
3. STDERR from kubectl sometimes has more details as to why starting a port forward fails, maybe pass that message on to the user.