Merge remote-tracking branch 'remotes/maxreitz/tags/pull-block-2020-07-21' into staging

Block patches for 5.1:
- Let LUKS images only be shared between VMs if the guest device was
  configured to allow that
- Fix abort() from bdrv_aio_cancel() for guest devices without a BDS

# gpg: Signature made Tue 21 Jul 2020 12:47:17 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-2020-07-21:
  block: fix bdrv_aio_cancel() for ENOMEDIUM requests
  qemu-iotests: add testcase for bz #1857490
  block/crypto: disallow write sharing by default

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