[bug#27521] [PATCH v5] build: Add iso9660 system image generator.

[Danny Milosavljevic]

> +(define* (iso9660-image #:key
[...]

> +           (mkdir-p "/tmp")

Also works without this.

> +           ;(mount "none" "/tmp" "tmpfs")

No idea why I don't have to do this. But it works.

> +           ;(mkdir-p "/tmp/extra")

> diff --git a/guix/scripts/system.scm b/guix/scripts/system.scm
> index 35675cc01..da0f5b04b 100644
> --- a/guix/scripts/system.scm
> +++ b/guix/scripts/system.scm
> @@ -578,7 +578,9 @@ PATTERN, a string.  When PATTERN is #f, display all the 
> system generations."
>                                                  (* 70 (expt 2 20)))
>                                              #:mappings mappings))
>      ((disk-image)
> -     (system-disk-image os #:disk-image-size image-size))))
> +     (system-disk-image os #:disk-image-size image-size))
> +    ((iso9660-disk-image)
> +     (system-disk-image os #:file-system-type "iso9660"))))

If we wanted, we also could replace disk-image by iso9660-disk-image entirely.  
It should also boot from USB (and from floppy if it fits there).

Do we want to?