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

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

# gpg: Signature made Mon 20 Jun 2016 15:05:24 BST
# gpg:                using RSA key 0x9CA4ABB381AB73C8
# gpg: Good signature from "Stefan Hajnoczi <stefanha@redhat.com>"
# gpg:                 aka "Stefan Hajnoczi <stefanha@gmail.com>"
# Primary key fingerprint: 8695 A8BF D3F9 7CDA AC35  775A 9CA4 ABB3 81AB 73C8

* remotes/stefanha/tags/block-pull-request:
  backup: follow AioContext change gracefully
  mirror: follow AioContext change gracefully
  blockjob: add AioContext attached callback
  block: use safe iteration over AioContext notifiers
  blockjob: add block_job_get_aio_context()
  blockjob: add pause points
  blockjob: rename block_job_is_paused()
  blockjob: move iostatus reset out of block_job_enter()
  block: process before_write_notifiers in bdrv_co_discard
  block: fix race in bdrv_co_discard with drive-mirror
  block: fixed BdrvTrackedRequest filling in bdrv_co_discard
  libqos: add qvirtqueue_cleanup()
  libqos: drop duplicated virtio_pci.h definitions
  libqos: drop duplicated virtio_scsi.h definitions
  libqos: drop duplicated virtio_blk.h definitions
  libqos: drop duplicated virtio_vring.h structs
  libqos: drop duplicated virtio_ring.h bit definitions
  libqos: drop duplicated virtio_config.h definitions
  libqos: drop duplicated PCI vendor ID definition
  libqos: use virtio_ids.h for device ID definitions

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