Warn if /sysroot is not read only

[travier]

See: coreos/fedora-coreos-tracker#1232

Add a warning if we find that /sysroot is not read only.

[dustymabe]

Hmm. Actually I think this doesn't belong in CLHM. Or maybe it could.

CLHM isn't focused on CoreOS so we need to be smart here. Either we find a way to easily have this not apply on systems where it doesn't make sense (i.e. Fedora Cloud or other) or we should just add this helper in our overlay. I even install CLHM on my desktop 🙂.

Aside: Wherever we add it let's tell the user how to disable the warning if they prefer like we've done with some other things. I think we did that with the cgroups v2 warning.

[travier]

Indeed. No problem moving this back to fedora-coreos-config or making this optional here..

[travier]

Moved to f-c-c.

[travier]

And moved back to CLHM. Although we might want it on all installations, having it here will make it easier to include / exclude this warning at the packaging level for different variants / distributions.