Block layer patches

# gpg: Signature made Wed 08 Jun 2016 09:31:38 BST
# gpg:                using RSA key 0x7F09B272C88F2FD6
# gpg: Good signature from "Kevin Wolf <kwolf@redhat.com>"

* remotes/kevin/tags/for-upstream: (31 commits)
  qemu-img bench: Add --flush-interval
  qemu-img bench: Implement -S (step size)
  qemu-img bench: Make start offset configurable
  qemu-img bench: Sequential writes
  qemu-img bench
  block: Don't emulate natively supported pwritev flags
  blockdev: clean up error handling in do_open_tray
  block: Fix bdrv_all_delete_snapshot() error handling
  qcow2: avoid extra flushes in qcow2
  raw-posix: Fetch max sectors for host block device
  block: assert that bs->request_alignment is a power of 2
  migration/block: Convert saving to BlockBackend
  migration/block: Convert load to BlockBackend
  block: Kill bdrv_co_write_zeroes()
  vmdk: Convert to bdrv_co_pwrite_zeroes()
  raw_bsd: Convert to bdrv_co_pwrite_zeroes()
  raw-posix: Convert to bdrv_co_pwrite_zeroes()
  qed: Convert to bdrv_co_pwrite_zeroes()
  gluster: Convert to bdrv_co_pwrite_zeroes()
  blkreplay: Convert to bdrv_co_pwrite_zeroes()
  ...
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>