Merge remote-tracking branch 'remotes/maxreitz/tags/pull-block-2020-03-26' into staging

Merge remote-tracking branch 'remotes/maxreitz/tags/pull-block-2020-03-26' into staging

Block patches for 5.0-rc1:
- Fix qemu-img convert with a host device or iscsi target
- Use-after-free fix in mirror
- Some minor qcow2 fixes
- Minor sheepdog fix
- Minor qemu-img check report fix

# gpg: Signature made Thu 26 Mar 2020 14:28:26 GMT
# gpg:                using RSA key 91BEB60A30DB3E8857D11829F407DB0061D5CF40
# gpg:                issuer "mreitz@redhat.com"
# gpg: Good signature from "Max Reitz <mreitz@redhat.com>" [full]
# Primary key fingerprint: 91BE B60A 30DB 3E88 57D1  1829 F407 DB00 61D5 CF40

* remotes/maxreitz/tags/pull-block-2020-03-26:
  iotests/138: Test leaks/corruptions fixed report
  iotests: Add poke_file_[bl]e functions
  qemu-img: Fix check's leak/corruption fix report
  sheepdog: Consistently set bdrv_has_zero_init_truncate
  qcow2: Avoid feature name extension on small cluster size
  qcow2: List autoclear bit names in header
  qcow2: Comment typo fixes
  block: trickle down the fallback image creation function use to the block drivers
  block: pass BlockDriver reference to the .bdrv_co_create
  block/mirror: fix use after free of local_err

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