Fix upgrades from grub2 < 1.99-4 (#735259)
    
    grub2 versions older than 1.99-4 had the following in %preun:
      # XXX Ugly
      rm -f /boot/%{name}/*.mod
      rm -f /boot/%{name}/*.img
      rm -f /boot/%{name}/*.lst
      rm -f /boot/%{name}/device.map
    
    This change tries to work around the damage caused on upgrades, by first
    backuping the files and later restoring them after the old packages's
    %preun has been run.
    
    Complements the change in 5c9195d.
    
    https://bugzilla.redhat.com/show_bug.cgi?id=735259