kvm: Fix test for boot images

The test have incorrect leftover of old limited implementation, now the system
shall update images by itself.

Also the typical scenario - image on first request - was not covered.

Adapt the test to code without needed linking.
2 jobs for fix/kvm-image-list-test in 0 seconds (queued for 1 second)
Status Job ID Name Coverage
  External
passed SlapOS.SoftwareReleases.IntegrationTest-luke/fix/kvm-image-list-test

03:37:38

failed SlapOS.SoftwareReleases.IntegrationTest-luke/fix/kvm-image-list-test

04:12:44