This update for grub2 fixes the following issues:

- Fix missing install device check in grub2-install on PowerPC which could lead
  to bootlist corruption (bsc#1221126)
    * add mandatoryminstallmdevicemcheckmformPowerPC
- Fix double free in xen booting if root filesystem is Btrfs (bsc#1259543)
    * btrfs: add ability to boot from subvolumes
    * btrfs: get default subvolume