Security update for xen (important)

This update for xen fixes the following issues:

Security issues fixed:

• CVE-2018-3665: Fix Lazy FP Save/Restore issue (XSA-267) (bsc#1095242).
• CVE-2018-12891: Fix possible Denial of Service (DoS) via certain PV MMU
  operations that affect the entire host (XSA-264) (bsc#1097521).
• CVE-2018-12892: Fix libxl to honour the readonly flag on HVM emulated
  SCSI disks (XSA-266) (bsc#1097523).
• CVE-2018-12893: Fix crash/Denial of Service (DoS) via safety check
  (XSA-265) (bsc#1097522).

Bug fixes:

• bsc#1027519: Add upstream patches from January.
• bsc#1098403: Fix regression introduced by changes for bsc#1079730. A PV
  domU without qcow2 and/or vfb has no qemu attached. Ignore QMP errors
  for PV domUs to handle PV domUs with and without an attached qemu-xen.
• bsc#1087289: Fix xen scheduler crash.

This update was imported from the SUSE:SLE-15:Update update project.