WIP: Nixos
Add support for NixOS images
- ssh_host_keys is supported
- adding site_key to authorized_keys is supported
- various NFS / autofs are NOT supported (home one is probably simple to add)
- login restriction is NOT supported
To test: kadeploy3 -f $OAR_NODEFILE -a http://public.nancy.grid5000.fr/~orichard/nixos-19.09.yaml -k