When a protected VM is created, the topmost level of page tables of its
ASCE is marked by the Ultravisor; any attempt to use that memory for
protected virtualization will result in failure.
Only a successful Destroy Configuration UVC will remove the marking.
When the Destroy Configuration UVC fails, the topmost level of page
tables of the VM does not get its marking cleared; to avoid issues it
must not be used again.
Since the page becomes in practice unusable, we set it aside and leak it.