Merge remote-tracking branch 'remotes/maxreitz/tags/pull-block-2020-04-07' into staging

Block patches for 5.0-rc2:
- Fix double QLIST_REMOVE() and potential request object leak in
  xen-block
- Prevent a potential assertion failure in qcow2's code for compressed
  clusters by rejecting invalid (unaligned) requests with -EIO
- Prevent discards on qcow2 v2 images from making backing data reappear
- Make qemu-img convert report I/O error locations by byte offsets
  consistently
- Fix for potential I/O test errors (accidental globbing due to missing
  quotes)

# gpg: Signature made Tue 07 Apr 2020 13:30:01 BST
# 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-2020-04-07:
  xen-block: Fix double qlist remove and request leak
  iotests/common.pattern: Quote echos
  qcow2: Check request size in qcow2_co_pwritev_compressed_part()
  qemu-img: Report convert errors by bytes, not sectors
  qcow2: Forbid discard in qcow2 v2 images with backing files

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