Nix VM with Debian + GUI

Username: `debian`
Password: `nixos`

0. Clean the VM:
`nh clean all`
`rm ~/.local/share/debian-vm/debian-persistent.qcow2`

1. Build the VM:
```bash
nix-build vm.nix -A system.build.customVM
```
2. Run the VM:
```bash
./result/bin/run-debian-vm
```
3. Watch it unravel:
```bash
ssh debian@localhost -p 2222
# Inside VM after SSH
cat /var/log/cloud-init-output.log
cat /var/log/cloud-init.log
ls -la /home/debian/
```