Merge remote-tracking branch 'remotes/stefanha/tags/block-pull-request' into staging

Block pull request

# gpg: Signature made Fri 31 Jan 2014 21:16:43 GMT using RSA key ID 81AB73C8
# gpg: Good signature from "Stefan Hajnoczi <stefanha@redhat.com>"
# gpg:                 aka "Stefan Hajnoczi <stefanha@gmail.com>"
# gpg: WARNING: This key is not certified with a trusted signature!
# gpg:          There is no indication that the signature belongs to the owner.
# Primary key fingerprint: 8695 A8BF D3F9 7CDA AC35  775A 9CA4 ABB3 81AB 73C8

* remotes/stefanha/tags/block-pull-request:
  qemu-iotests: only run 071 on qcow2
  dataplane: Comment fix
  block/vhdx: Error checking fixes
  qemu-iotests: Drop assert_no_active_commit in case 040
  block/vmdk: add basic .bdrv_check support
  block: remove qcow2 .bdrv_make_empty implementation
  block: remove QED .bdrv_make_empty implementation
  Describe flaws in qcow/qcow2 encryption in the docs

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