Security update for xen (important)

This update for xen fixes several issues.

These security issues were fixed:

• CVE-2017-14316: Missing bound check in function alloc_heap_pages for
  an internal array allowed attackers using crafted hypercalls to execute
  arbitrary code within Xen (XSA-231, bsc#1056278)
• CVE-2017-14318: The function __gnttab_cache_flush missed a check for
  grant tables, allowing a malicious guest to crash the host or for x86 PV
  guests to potentially escalate privileges (XSA-232, bsc#1056280)
• CVE-2017-14317: A race in cxenstored may have cause a double-free
  allowind for DoS of the xenstored daemon (XSA-233, bsc#1056281).
• CVE-2017-14319: An error while handling grant mappings allowed malicious
  or buggy x86 PV guest to escalate its privileges or crash the hypervisor
  (XSA-234, bsc#1056282).

These non-security issues were fixed:

• bsc#1057358: Fixed boot into SUSE Linux Enterprise 12.3 with secure boot
• bsc#1055695: Fixed restoring updates for HVM guests for ballooned domUs