Merge remote-tracking branch 'remotes/vsementsov/tags/pull-jobs-2021-10-07-v2' into staging

mirror: Handle errors after READY cancel
v2: add small fix by Stefano, Hanna's series fixed

# gpg: Signature made Thu 07 Oct 2021 08:25:07 AM PDT
# gpg:                using RSA key 8B9C26CDB2FD147C880E86A1561F24C1F19F79FB
# gpg: Good signature from "Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>" [unknown]
# gpg: WARNING: This key is not certified with a trusted signature!
# gpg:          There is no indication that the signature belongs to the owner.
# Primary key fingerprint: 8B9C 26CD B2FD 147C 880E  86A1 561F 24C1 F19F 79FB

* remotes/vsementsov/tags/pull-jobs-2021-10-07-v2:
  iotests: Add mirror-ready-cancel-error test
  mirror: Do not clear .cancelled
  mirror: Stop active mirroring after force-cancel
  mirror: Check job_is_cancelled() earlier
  mirror: Use job_is_cancelled()
  job: Add job_cancel_requested()
  job: Do not soft-cancel after a job is done
  jobs: Give Job.force_cancel more meaning
  job: @force parameter for job_cancel_sync()
  job: Force-cancel jobs in a failed transaction
  mirror: Drop s->synced
  mirror: Keep s->synced on error
  job: Context changes in job_completed_txn_abort()
  block/aio_task: assert `max_busy_tasks` is greater than 0
  block/backup: avoid integer overflow of `max-workers`

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>