kubernetes.py: prune_local_images: don't remove parent images

Don't delete parent images of live incremental images. This avoids
triggering full image builds when scap clean-images is followed by
scap sync-world.

This relies on a label added by release!202 (merged)

I removed the parallel execution code for simplicity. It would be
reasonable to revive it for the image removal phase of the operation,
but parallel operation is not necessary for the mark phase.

Merge request reports

Loading