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

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

# gpg: Signature made Thu 08 Feb 2018 01:29:22 GMT
# gpg:                using RSA key CA35624C6A9171C6
# gpg: Good signature from "Fam Zheng <famz@redhat.com>"
# Primary key fingerprint: 5003 7CB7 9706 0F76 F021  AD56 CA35 624C 6A91 71C6

* remotes/famz/tags/staging-pull-request:
  docs: Add docs/devel/testing.rst
  qapi: Add NVMe driver options to the schema
  docs: Add section for NVMe VFIO driver
  block: Move NVMe constants to a separate header
  qemu-img: Map bench buffer
  block/nvme: Implement .bdrv_(un)register_buf
  block: Introduce buf register API
  block: Add VFIO based NVMe driver
  util: Introduce vfio helpers
  stubs: Add stubs for ram block API
  curl: convert to CoQueue
  coroutine-lock: make qemu_co_enter_next thread-safe
  coroutine-lock: convert CoQueue to use QemuLockable
  lockable: add QemuLockable
  test-coroutine: add simple CoMutex test
  docker: change Fedora base image to fedora:27

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