Merge remote-tracking branch 'remotes/jnsnow/tags/ide-pull-request' into staging

# gpg: Signature made Fri 13 Nov 2015 20:16:21 GMT using RSA key ID AAFC390E
# gpg: Good signature from "John Snow (John Huston) <jsnow@redhat.com>"

* remotes/jnsnow/tags/ide-pull-request:
  qtest/ahci: use raw format when qemu-img is absent
  libqos: add qemu-img presence check
  qtest/ahci: always specify image format
  ahci/qtest: don't use tcp sockets for migration tests
  atapi: Prioritize unknown cmd error over BCL error
  atapi: add byte_count_limit helper

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