Security update for xen (important)

This update for xen fixes several issues.

These security issues were fixed:

• CVE-2017-2620: In CIRRUS_BLTMODE_MEMSYSSRC mode the bitblit copy routine
  cirrus_bitblt_cputovideo failed to check the memory region, allowing for
  an out-of-bounds write that allows for privilege escalation
  (bsc#1024834).
• CVE-2017-2615: An error in the bitblt copy operation could have allowed
  a malicious guest administrator to cause an out of bounds memory access,
  possibly leading to information disclosure or privilege escalation
  (bsc#1023004).
• A malicious guest could have, by frequently rebooting over extended
  periods of time, run the host system out of memory, resulting in a
  Denial of Service (DoS) (bsc#1022871)
• CVE-2016-9921: The Cirrus CLGD 54xx VGA Emulator support was vulnerable
  to a divide by zero issue while copying VGA data. A privileged user
  inside guest could have used this flaw to crash the process instance on
  the host, resulting in DoS (bsc#1015169

These non-security issues were fixed:

• bsc#1000195: Prevent panic on CPU0 while booting on SLES 11 SP3
• bsc#1002496: Added support for reloading clvm in block-dmmd block-dmmd
• bsc#1005028: Fixed building Xen RPMs from Sources