Merge remote-tracking branch 'remotes/maxreitz/tags/pull-block-2019-10-10' into staging

Block patches:
- Parallelized request handling for qcow2
- Backup job refactoring to use a filter node instead of before-write
  notifiers
- Add discard accounting information to file-posix nodes
- Allow trivial reopening of nbd nodes
- Some iotest fixes

# gpg: Signature made Thu 10 Oct 2019 12:40:34 BST
# gpg:                using RSA key 91BEB60A30DB3E8857D11829F407DB0061D5CF40
# gpg:                issuer "[email protected]"
# gpg: Good signature from "Max Reitz <[email protected]>" [full]
# Primary key fingerprint: 91BE B60A 30DB 3E88 57D1  1829 F407 DB00 61D5 CF40

* remotes/maxreitz/tags/pull-block-2019-10-10: (36 commits)
  iotests/162: Fix for newer Linux 5.3+
  tests: fix I/O test for hosts defaulting to LUKSv2
  nbd: add empty .bdrv_reopen_prepare
  block/backup: use backup-top instead of write notifiers
  block: introduce backup-top filter driver
  block/block-copy: split block_copy_set_callbacks function
  block/backup: move write_flags calculation inside backup_job_create
  block/backup: move in-flight requests handling from backup to block-copy
  iotests: Use stat -c %b in 125
  iotests: Disable 125 on broken XFS versions
  iotests: Fix 125 for growth_mode = metadata
  qapi: query-blockstat: add driver specific file-posix stats
  file-posix: account discard operations
  scsi: account unmap operations
  scsi: move unmap error checking to the complete callback
  scsi: store unmap offset and nb_sectors in request struct
  ide: account UNMAP (TRIM) operations
  block: add empty account cookie type
  qapi: add unmap to BlockDeviceStats
  qapi: group BlockDeviceStats fields
  ...

Signed-off-by: Peter Maydell <[email protected]>