Move the ostree repository and the tar image to the root of the
boot iso. This has several advantages: we do no longer have to
correctly guess the size of the anaconda image. Also we do not
need to compress the payload within the squashfs.
Update the image installer's test data. NB: the changes to the
package list were introduced earlier and should mostly affect
the build pipeline. Should have caught is in the corresponding
change, but was apparently not picked up by CI.
3dfc997992