This fixes `clan ssh` with the `--json` and `--png` flags.
It will now correctly use the actual fields that are present in the
generated json.
- probes if the ports are accessible
- if accessible will attempt a single ssh connection with the provided
password, in order to not spam ssh attempts
Fixes#1177
This makes the function usage less confusing (you can now tell from the call side what are flags and what is passed to nix-shell) and allows to use different flakes to download packages.
