Wrong UEFI entries created by agent installer when not using RHCOS

Description of problem:

When nodes boot via UEFI and the agent-installer performs an installation not using RHCOS as base os (as in Sprint 249/250 where CentOS is in use), the default uefi entry is created and set as default, but it targets [EFI]/redhat/shim* instead of [EFI]/{centos|fedora}/shim*.

This might be due to https://github.com/openshift/assisted-installer/blob/master/src/ops/ops.go#L251-L261

Version-Release number of selected component (if applicable):

4.16

How reproducible:

Always, when not using RHCOS as base os

Steps to Reproduce:

    1. Configure baremetal nodes to boot via UEFI
    2. Install OCP through the agent installation while base os is not RHCOS (Like in Sprint 249/250 where base os is CentOS Stream)
    3.
    

Actual results:

Baremetal hosts fail to boot from disk due to EFI mismatch

Expected results:

Baremetal hosts boot correctly

Additional info: