Merge remote-tracking branch 'remotes/hreitz-gitlab/tags/pull-block-2022-02-01' into staging

Block patches:
- Add support to the iotests to test qcow2's zstd compression mode
- Fix post-migration block node permissions
- iotests fixes (051 and mirror-ready-cancel-error)
- Remove an outdated comment

# gpg: Signature made Tue 01 Feb 2022 13:34:54 GMT
# gpg:                using RSA key CB62D7A0EE3829E45F004D34A1FA40D098019CDF
# gpg:                issuer "hreitz@redhat.com"
# gpg: Good signature from "Hanna Reitz <hreitz@redhat.com>" [marginal]
# gpg: WARNING: This key is not certified with sufficiently trusted signatures!
# gpg:          It is not certain that the signature belongs to the owner.
# Primary key fingerprint: CB62 D7A0 EE38 29E4 5F00  4D34 A1FA 40D0 9801 9CDF

* remotes/hreitz-gitlab/tags/pull-block-2022-02-01: (24 commits)
  block.h: remove outdated comment
  iotests/migration-permissions: New test
  block-backend: Retain permissions after migration
  iotests: declare lack of support for compresion_type in IMGOPTS
  iotest 214: explicit compression type
  iotests 60: more accurate set dirty bit in qcow2 header
  iotests: bash tests: filter compression type
  iotest 39: use _qcow2_dump_header
  iotests: massive use _qcow2_dump_header
  iotests/common.rc: introduce _qcow2_dump_header helper
  qcow2: simple case support for downgrading of qcow2 images with zstd
  iotest 302: use img_info_log() helper
  iotests.py: filter compression type out
  iotests.py: filter out successful output of qemu-img create
  iotest 065: explicit compression type
  iotest 303: explicit compression type
  iotests.py: rewrite default luks support in qemu_img
  iotests: drop qemu_img_verbose() helper
  iotests.py: qemu_img*("create"): support IMGOPTS='compression_type=zstd'
  iotests: specify some unsupported_imgopts for python iotests
  ...

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