bug#37164: Generated installation image does not include grub.

[Jesse Gibbons <jgibbons2357@gmail.com>]

1. generate the install image
 guix system disk-image --file-system-type=iso9600 --verbosity=3 --
root=installation-os-x86_64.iso  --system=x86_64-linux -e '(@ (gnu
system install) installation-os)'

2. examine the resulting iso
readlink installation-os-x86_64.iso | xargs file

output: /gnu/store/3xp541s4zrxass6h6rcwfz7bc33wv84p-disk-image: DOS/MBR
boot sector; partition 1 : ID=0x83, active, start-CHS (0x0,32,33), end-
CHS (0xe3,198,58), startsector 2048, 3657239 sectors; partition 2 :
ID=0xef, start-CHS (0xe3,198,59), end-CHS (0xe8,224,16), startsector
3659287, 81921 sectors

3. Compare this output with what file says about the official
installation iso:
wget https://ftp.gnu.org/gnu/guix/guix-system-install-1.0.1.x86_64-linu
x.iso.xz
unxz guix-system-install-1.0.1.x86_64-linux.iso.xz
readlink guix-system-install-1.0.1.x86_64-linux.iso

output:guix-system-install-1.0.1.x86_64-linux.iso: DOS/MBR boot sector;
GRand Unified Bootloader, stage1 version 0x79, boot drive 0xbb, stage2
address 0x8e70, 1st sector stage2 0xb8db31c3, stage2 segment 0x201;
partition 1 : ID=0xee, start-CHS (0x0,0,2), end-CHS (0x3f6,38,4),
startsector 1, 2694403 sectors, extended partition table (last)

It appears file discovered the GRand Unified Bootloader in the official
iso but not in the generated iso.

When I try to use the generated iso in virt-manager, it claims there
are no bootable drives. I think this is because the generated iso has
no GRUB.

The manual says to specify the file gnu/system/install.scm instead of
the value (@ (gnu system install) installation-os)) but ultimately they
give guix the same value, so I think that wouldn't make a difference.

removing --system=x86_64 does not trigger a full rebuild, so it looks
like guix does not expect to build anything different.

Guix describe outputs:

Generation 47	Aug 23 2019 09:22:24	(current)
  guix d78bc23
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: master
    commit: d78bc23411b1351ff9495a511c22b27d17f9226f

GUIX_PACKAGE_PATH="/home/jesse/Documents/broken-guix/Broken-Guix-
Packages"

Thanks
-Jesse