Block layer patches

# gpg: Signature made Fri 22 Dec 2017 14:09:01 GMT
# gpg:                using RSA key 0x7F09B272C88F2FD6
# gpg: Good signature from "Kevin Wolf <kwolf@redhat.com>"
# Primary key fingerprint: DC3D EB15 9A9A F95D 3D74  56FE 7F09 B272 C88F 2FD6

* remotes/kevin/tags/for-upstream: (35 commits)
  block: Keep nodes drained between reopen_queue/multiple
  commit: Simplify reopen of base
  test-bdrv-drain: Test graph changes in drained section
  block: Allow graph changes in subtree drained section
  test-bdrv-drain: Recursive draining with multiple parents
  test-bdrv-drain: Test behaviour in coroutine context
  test-bdrv-drain: Tests for bdrv_subtree_drain
  block: Add bdrv_subtree_drained_begin/end()
  block: Don't notify parents in drain call chain
  test-bdrv-drain: Test nested drain sections
  block: Nested drain_end must still call callbacks
  block: Don't block_job_pause_all() in bdrv_drain_all()
  test-bdrv-drain: Test drain vs. block jobs
  blockjob: Pause job on draining any job BDS
  test-bdrv-drain: Test bs->quiesce_counter
  test-bdrv-drain: Test callback for bdrv_drain
  block: Make bdrv_drain() driver callbacks non-recursive
  block: Assert drain_all is only called from main AioContext
  block: Remove unused bdrv_requests_pending
  block: Mention -drive cyls/heads/secs/trans/serial/addr in deprecation chapter
  ...

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