Now that LinuxKit works on a truly immutable filesystem, for an
ISO it makes sense to use the ISO filesystem rather than using
an initrd. Only major difference is you may need to specify the
device for the root filesystem in the kernel command line, but
we set a sane default of `/dev/sr0` if unspecified.
Signed-off-by: Justin Cormack <justin.cormack@docker.com>
Previously we hardcoded `bzImage` which is not used for all
use cases or architectures.
fix#1630
Signed-off-by: Justin Cormack <justin.cormack@docker.com>
