Add feature to remove cd-rom that was used for unmount_iso

[npdev453]

unmount_iso did not remove cd-rom that whas used for building from iso but in sometimes template should not have any cd-roms

[mpywell]

I think this is especially needed for additional_iso_files blocks, current builds with one or more additional_iso_files blocks end up with at least two (boot ISO and one or more additional_iso_files) cdrom devices attached to the template output.

Thoughts on making the behaviour of unmount = true for additional_iso_files blocks also remove the cdrom device? For the boot ISO device (ide2) I could see the value in keeping one cdrom device attached to a template by default, maybe removing ide2 could be an opt-in setting.