coreos-installer install tries to modify grub.cfg to apply console settings even on s390x

[jlebon]

Bug

coreos-installer Version

v0.17.0

Expected Behavior

On s390x, since there's no GRUB config, using coreos-installer install --console or the console key in installer dropins only sets the appropriate karg and doesn't try to look for a GRUB config.

Actual Behavior

On s390x, coreos-installer install --console or the console key in installer dropins tries to look for a GRUB config that doesn't exist and fails the install.

Reproduction Steps

1. Run coreos-installer install --console on s390x.

Other Information

Output:

coreos-installer install --config-file /etc/coreos/installer.d/mantle.yaml --fetch-retries infinite
Running with arguments: --image-url http://10.0.2.2:34353/fedora-coreos-38.20230419.dev.0-metal.s390x.raw.xz --ignition-file /var/opt/pointer.ign --console ttysclp0 --insecure /dev/vda --fetch -retries infinite
Downloading image from http://10.0.2.2:34353/fedora-coreos-38.20230419.dev.0-metal.s390x.raw.xz
Downloading signature from http://10.0.2.2:34353/fedora-coreos-38.20230419.dev.0-metal.s390x.raw.xz.sig
Failed to fetch signature: fetching signature URL
Signature not found; skipping verification as requested
...
Read disk 479.3 MiB/479.3 MiB (100%)
Writing Ignition config
Error: configuring console
Caused by:
    0: reading grub.cfg
    1: No such file or directory (os error 2)
Resetting partition table
Error: install failed