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

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

Block layer patches:

- qcow2: Fix preallocation on block devices
- backup: Make sure that source and target size match
- vmdk: Fix zero cluster handling
- Follow-up cleanups and fixes for the truncate changes
- iotests: Skip more tests if required drivers are missing

# gpg: Signature made Fri 08 May 2020 13:39:55 BST
# gpg:                using RSA key DC3DEB159A9AF95D3D7456FE7F09B272C88F2FD6
# gpg:                issuer "kwolf@redhat.com"
# 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: (30 commits)
  block: Drop unused .bdrv_has_zero_init_truncate
  vhdx: Rework truncation logic
  parallels: Rework truncation logic
  ssh: Support BDRV_REQ_ZERO_WRITE for truncate
  sheepdog: Support BDRV_REQ_ZERO_WRITE for truncate
  rbd: Support BDRV_REQ_ZERO_WRITE for truncate
  nfs: Support BDRV_REQ_ZERO_WRITE for truncate
  file-win32: Support BDRV_REQ_ZERO_WRITE for truncate
  gluster: Drop useless has_zero_init callback
  qcow2: Fix preallocation on block devices
  iotests/055: Use cache.no-flush for vmdk target
  iotests: Backup with different source/target size
  backup: Make sure that source and target size match
  backup: Improve error for bdrv_getlength() failure
  iotests/283: Use consistent size for source and target
  iotests: vmdk: Enable zeroed_grained=on by default
  vmdk: Flush only once in vmdk_L2update()
  vmdk: Don't update L2 table for zero write on zero cluster
  vmdk: Fix partial overwrite of zero cluster
  vmdk: Fix zero cluster allocation
  ...

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