Merge remote-tracking branch 'remotes/kevin/tags/for-upstream' into staging

Block layer patches:

- Fix another case of mirror block job deadlocks
- Minor fixes

# gpg: Signature made Fri 27 Mar 2020 15:18:37 GMT
# gpg:                using RSA key 7F09B272C88F2FD6
# 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:
  qcow2: Remove unused fields from BDRVQcow2State
  mirror: Wait only for in-flight operations
  Revert "mirror: Don't let an operation wait for itself"
  nvme: Print 'cqid' for nvme_del_cq
  block: fix bdrv_root_attach_child forget to unref child_bs
  block/iscsi:use the flags in iscsi_open() prevent Clang warning

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