Merge remote-tracking branch 'remotes/maxreitz/tags/pull-block-2019-07-22' into staging

Merge remote-tracking branch 'remotes/maxreitz/tags/pull-block-2019-07-22' into staging

Block patches for 4.1.0-rc2:
- NVMe block driver fixes
- Drain/AioContext fixes

# gpg: Signature made Mon 22 Jul 2019 17:44:45 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-2019-07-22:
  block: Only the main loop can change AioContexts
  block: Dec. drained_end_counter before bdrv_wakeup
  block/nvme: don't touch the completion entries
  block/nvme: support larger that 512 bytes sector devices
  block/nvme: fix doorbell stride

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