Unification of boot loader updates, phase 1

Let's track what's needed to do for this change here. See: https://fedoraproject.org/wiki/Changes/BootLoaderUpdatesPhase1

The initial changes landed in the grub2 packages:

• https://src.fedoraproject.org/rpms/grub2/pull-request/136
• https://src.fedoraproject.org/rpms/grub2/pull-request/138

But this is failing in CoreOS builds: https://jenkins-coreos-ci.apps.ocp.fedoraproject.org/blue/organizations/jenkins/test-override/detail/test-override/1369/pipeline/113/

I have not investigated yet if it's just a missing directory.