withDriveLetters

In case you haven't run into this 
```
error: function 'anonymous lambda' called with unexpected argument 'withDriveLetters'
       at /nix/store/qp84z14bxpd6mxk3ksg7gqq4vb2w8ssy-source/lib/runners/cloud-hypervisor.nix:1:1:
```

when using cloud hypervisor. I could try to fix this or next weekend, but better if someone that knows what they're doing looks at it, for now I'll revert.