Prior this commit the ami image type produced raw.xz images. This was bad for
two reasons:
- The upload was broken because AWS doesn't support tar.xz format
- XZ compression is terribly slow
This commit changes the format to vhdx, which is supported by AWS and also
quite quick. See https://github.com/osbuild/osbuild-composer/issues/257
why vhdx was chosen.
Fixes#257