distro/fedora: install kernel and bootloader in ostree commits

This is a partial revert of 006c5b26, where kernel settings and bootloaders were only
installed on bootable systems.

However, ostree-based systems need the ability to pick up kernels and bootloaders from
the commit to install on the instance, so make this conditional on being bootable or an
ostree commit. This is probably an indication that we need a different abstraction.

internal/distro/fedora/manifests.go

@@ -229,7 +229,9 @@ func osPipeline(m *manifest.Manifest,
 			return nil, err
 		}
 		pl.PartitionTable = pt
+	}
 
+	if t.bootable || t.rpmOstree {
 		if t.supportsUEFI() {
 			pl.UEFIVendor = t.arch.distro.vendor
 		}