Set up /etc/sub{g,u}id on install, since we're creating a root and a ${USER} account anyway

This would help make boulder work ootb.

```bash
sudo touch /etc/sub{uid,gid}
sudo usermod --add-subuids 1000000-1065535 --add-subgids 1000000-1065535 root
sudo usermod --add-subuids 1065536-1131071 --add-subgids 1065536-1131071 "$USER"
```