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

Block layer patches:

- iscsi: Cap block count from GET LBA STATUS (CVE-2020-1711)
- AioContext fixes in QMP commands for backup and bitmaps
- iotests fixes

# gpg: Signature made Mon 27 Jan 2020 17:49:58 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:
  iscsi: Don't access non-existent scsi_lba_status_descriptor
  iscsi: Cap block count from GET LBA STATUS (CVE-2020-1711)
  block/backup: fix memory leak in bdrv_backup_top_append()
  iotests: Test handling of AioContexts with some blockdev actions
  blockdev: Return bs to the proper context on snapshot abort
  blockdev: Acquire AioContext on dirty bitmap functions
  block/backup-top: Don't acquire context while dropping top
  blockdev: honor bdrv_try_set_aio_context() context requirements
  blockdev: unify qmp_blockdev_backup and blockdev-backup transaction paths
  blockdev: unify qmp_drive_backup and drive-backup transaction paths
  blockdev: fix coding style issues in drive_backup_prepare
  iotests: Add more "skip_if_unsupported" statements to the python tests
  iotests.py: Let wait_migration wait even more

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