Merge remote-tracking branch 'remotes/dgilbert/tags/pull-migration-20181011a' into...

Migration pull 2018-10-11

With one bonus HMP fix.

# gpg: Signature made Thu 11 Oct 2018 20:23:12 BST
# gpg:                using RSA key 0516331EBC5BFDE7
# gpg: Good signature from "Dr. David Alan Gilbert (RH2) <dgilbert@redhat.com>"
# Primary key fingerprint: 45F5 C71B 4A0C B7FB 977A  9FA9 0516 331E BC5B FDE7

* remotes/dgilbert/tags/pull-migration-20181011a:
  migration-test: Only generate a single target architecture
  qmp, hmp: make subsystem/system-vendor identities optional
  vhost-user: Don't ask for reply on postcopy mem table set
  vhost-user: Fix userfaultfd leak
  migration: Stop postcopy fault thread before notifying
  tests/migration: Enable the migration test on s390x, too
  tests: Add migration test for aarch64

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