Merge remote-tracking branch 'remotes/maxreitz/tags/pull-block-2020-07-27' into staging

Block patches for 5.1:
- Coverity fix
- iotests fix for rx and avr
- iotests fix for qcow2 -o compat=0.10

# gpg: Signature made Mon 27 Jul 2020 15:36:23 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-2020-07-27:
  iotests/197: Fix for compat=0.10
  iotests: Select a default machine for the rx and avr targets
  block/amend: Check whether the node exists

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