Merge remote-tracking branch 'remotes/bonzini/tags/for-upstream' into staging

Merge remote-tracking branch 'remotes/bonzini/tags/for-upstream' into staging

Bug fixes.

# gpg: Signature made Tue 17 Jul 2018 16:06:07 BST
# gpg:                using RSA key BFFBD25F78C7AE83
# gpg: Good signature from "Paolo Bonzini <bonzini@gnu.org>"
# gpg:                 aka "Paolo Bonzini <pbonzini@redhat.com>"
# Primary key fingerprint: 46F5 9FBD 57D6 12E7 BFD4  E2F7 7E15 100C CD36 69B1
#      Subkey fingerprint: F133 3857 4B66 2389 866C  7682 BFFB D25F 78C7 AE83

* remotes/bonzini/tags/for-upstream:
  Document command line options with single dash
  opts: remove redundant check for NULL parameter
  i386: only parse the initrd_filename once for multiboot modules
  i386: fix regression parsing multiboot initrd modules
  virtio-scsi: fix hotplug ->reset() vs event race
  qdev: add HotplugHandler->post_plug() callback
  hw/char/serial: retry write if EAGAIN
  PC Chipset: Improve serial divisor calculation
  vhost-user-test: added proper TestServer *dest initialization in test_migrate()
  hyperv: ensure VP index equal to QEMU cpu_index
  hyperv: rename vcpu_id to vp_index
  accel: Fix typo and grammar in comment
  dump: add kernel_gs_base to QEMU CPU state

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