Fix EFI boot entry shown "fedora" issue

Actually the EFI boot entry should show "oVirt Node Hypervisor",not
"fedora" value.
Also this patch fixed using wrong loader_filename issue.
(For fedora, the loader_filename should be "grubx64.efi."
 For rhel, the loader_filename should be "grub.efi")

Change-Id: Ia326f049cbea64e646a974105f265a22c45f315f
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1004120
Signed-off-by: hadong <hadong0720@gmail.com>