- manual filename entry if the iso cannot be found
- manual selection from multiple debian isos
- register the partition and drive that the iso is mounted from as
  ones that should not be formatted, installed to or partitioned.
  Partconf has an undocumented, and maybe working directory in /var that
  can contain scripts that return false if a partition is not to be used.
  partitioner may not have anything, and autopartkit would also need mods.