Use a dummy LUKS key file in installTest

[Kranzes]

If in your disko configuraiton you don't use the keyFile option for LUKS and you prefer entering the passphrase interactively, installTest would hang as it will wait for user interaction. I think that for the installTest we should make it set a dummy password if not keyFile is provided, that way the test actually runs.

[Lassulus]

https://github.com/nix-community/disko/pull/314

[Kranzes]

I haven't test this yet but I was thinking that maybe a default behavior would be nice to have when LUKS is detected. If a device that uses LUKS is detected it will automatically set settings.keyFile for it in the test's config.