Merge remote-tracking branch 'remotes/stefanha/tags/block-pull-request' into staging

Pull request

Changelog: No user-visible changes.

# gpg: Signature made Thu 24 Jan 2019 10:28:53 GMT
# gpg:                using RSA key 9CA4ABB381AB73C8
# gpg: Good signature from "Stefan Hajnoczi <stefanha@redhat.com>"
# gpg:                 aka "Stefan Hajnoczi <stefanha@gmail.com>"
# Primary key fingerprint: 8695 A8BF D3F9 7CDA AC35  775A 9CA4 ABB3 81AB 73C8

* remotes/stefanha/tags/block-pull-request:
  qemu-coroutine-sleep: drop CoSleepCB
  iotests: add 238 for throttling tgm unregister iothread segfault
  throttle-groups: fix restart coroutine iothread race

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