stboot: Add cdrom support to host-config
Created by: bjoto
Add "cdrom:" prefix support for the -host-config flag. This will make stboot mounting /dev/sr0, and look for the host configuration at the provided path.
Also rework the retry mechanism, so it is more generic and support cdrom mounts in addition to GPT mounts.
An example: -host-config=cdrom:/host_configuration.json
Signed-off-by: Björn Töpel bjorn@mullvad.net