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