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

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

Pull request

The following disk I/O throttling fixes solve recent bugs.

# gpg: Signature made Tue 14 Nov 2017 10:37:12 GMT
# gpg:                using RSA key 0x9CA4ABB381AB73C8
# 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-iotests: Test I/O limits with removable media
  block: Leave valid throttle timers when removing a BDS from a backend
  block: Check for inserted BlockDriverState in blk_io_limits_disable()
  throttle-groups: drain before detaching ThrottleState
  block: all I/O should be completed before removing throttle timers.

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