Security update for grub2 (important)

This update for grub2 provides the following fixes and enhancements:

Security issue fixed:

• Fix buffer overflows when reading username and password. (bsc#956631,
  CVE-2015-8370)

Non security issues fixed:

• Expand list of grub.cfg search path in PV Xen guests for systems
  installed
  on btrfs snapshots. (bsc#946148, bsc#952539)
• Add --image switch to force zipl update to specific kernel. (bsc#928131)
• Do not use shim lock protocol for reading PE header as it won’t be
  available when secure boot is disabled. (bsc#943380)
• Make firmware flaw condition be more precisely detected and add debug
  message for the case.