admin: Error out if we see malformed or mismatched checksums for /boot

The kernel/initramfs both need to end in -SHA256 and match.
tests: Drop kernel modules from checksums

We can actually share these across different kernels.  Thanks to
Tobias Hunger <tobias.hunger@gmail.com> for pointing this out.
Configure: Add buildopt for arch modules and switch-root
Add support for arch linux