Update to efibootmgr 15
    Make efibootmgr use EFIDIR / efibootmgr.efidir like fwupdate does
    make --loader default build-time configurable
    sanitize set_mirror()/get_mirror()
    Add support for parsing loader options as UCS2
    GCC 7 fixes
    Don't use -fshort-wchar since we don't run on EFI machines.
    Also rebuild for efivar-31-1.fc26 to get symbol versioning right.
      Resolves: rhbz#1468841
    
    Signed-off-by: Peter Jones <pjones@redhat.com>