
Ubuntu images in 12.04 added the user to the 'admin' group. The admin group was deprecated/replaced with the 'sudo' group in 12.10. d-i adds its first-user to the 'sudo' group, so it makes sense to mimic that behavior for the default user created by cloud-init. That was the original reason behind the presense in the 'admin' group. Also, here I sorted alphabetically the group list.