Block layer patches

- Supporting changing 'file' in x-blockdev-reopen
- ssh: add support for sha256 host key fingerprints
- vhost-user-blk: Implement reconnection during realize
- introduce QEMU_AUTO_VFREE
- Don't require password of encrypted backing file for image creation
- Code cleanups

# gpg: Signature made Wed 30 Jun 2021 17:00:55 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: (24 commits)
  vhost-user-blk: Implement reconnection during realize
  vhost-user-blk: Factor out vhost_user_blk_realize_connect()
  vhost: Distinguish errors in vhost_dev_get_config()
  vhost-user-blk: Add Error parameter to vhost_user_blk_start()
  vhost: Return 0/-errno in vhost_dev_init()
  vhost: Distinguish errors in vhost_backend_init()
  vhost: Add Error parameter to vhost_dev_init()
  block/ssh: add support for sha256 host key fingerprints
  block/commit: use QEMU_AUTO_VFREE
  introduce QEMU_AUTO_VFREE
  iotests: Test replacing files with x-blockdev-reopen
  block: Allow changing bs->file on reopen
  block: BDRVReopenState: drop replace_backing_bs field
  block: move supports_backing check to bdrv_set_file_or_backing_noperm()
  block: bdrv_reopen_parse_backing(): simplify handling implicit filters
  block: bdrv_reopen_parse_backing(): don't check frozen child
  block: bdrv_reopen_parse_backing(): don't check aio context
  block: introduce bdrv_set_file_or_backing_noperm()
  block: introduce bdrv_remove_file_or_backing_child()
  block: comment graph-modifying function not updating permissions
  ...

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