Merge remote-tracking branch 'remotes/otubo/tags/pull-seccomp-20180823' into staging

pull-seccomp-20180823

# gpg: Signature made Thu 23 Aug 2018 15:46:13 BST
# gpg:                using RSA key DF32E7C0F0FFF9A2
# gpg: Good signature from "Eduardo Otubo (Senior Software Engineer) <otubo@redhat.com>"
# Primary key fingerprint: D67E 1B50 9374 86B4 0723  DBAB DF32 E7C0 F0FF F9A2

* remotes/otubo/tags/pull-seccomp-20180823:
  seccomp: set the seccomp filter to all threads
  configure: require libseccomp 2.2.0
  seccomp: prefer SCMP_ACT_KILL_PROCESS if available
  seccomp: use SIGSYS signal instead of killing the thread

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>