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

Block layer patches:

- iotests: Fix output of qemu-io related tests
- Don't ignore bdrv_set_aio_context() for nodes with bs->drv = NUL
- vmdk: Set vmdk parent backing_format to vmdk
- qcow2: Preallocation fixes (especially for external data files)
- Add linear-buffer-based APIs (as wrappers around qiov-based ones)
- Various code cleanups and small corner case fixes

# gpg: Signature made Tue 30 Apr 2019 16:35:09 BST
# gpg:                using RSA key 7F09B272C88F2FD6
# gpg: Good signature from "Kevin Wolf <kwolf@redhat.com>" [full]
# Primary key fingerprint: DC3D EB15 9A9A F95D 3D74  56FE 7F09 B272 C88F 2FD6

* remotes/kevin/tags/for-upstream: (27 commits)
  block/qed: add missed coroutine_fn markers
  iotests: Check that images are in read-only mode after block-commit
  commit: Make base read-only if there is an early failure
  qemu-img: use buffer-based io
  block/stream: use buffer-based io
  block/commit: use buffer-based io
  block/backup: use buffer-based io
  block/parallels: use buffer-based io
  block/qed: use buffer-based io
  block/qcow: use buffer-based io
  block/qcow2: use buffer-based io
  block: introduce byte-based io helpers
  qcow2: Fix error handling in the compression code
  qcow2: Fix qcow2_make_empty() with external data file
  qemu-img: Make create hint at protocol options
  iotests: Perform the correct test in 082
  qcow2: Fix full preallocation with external data file
  qcow2: Add errp to preallocate_co()
  qcow2: Avoid COW during metadata preallocation
  qemu-img: Saner printing of large file sizes
  ...

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