Flasher images for aliased device types not identified

[alexgg]

When using flasher images that have a different slug than machine name (like intel-nuc/genericx86-64), the logic that identifies a flasher image fails because it looks for a balena-image-<slug>.img> instead of balena-image-.img` which is the actual artifact name.

I work around it by using the non-flasher image. The fix is probably to parse contracts or call the API to map them