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

Block/testing patches

v2: Fix URL.
    Drop BSD patch.

# gpg: Signature made Wed 09 Jan 2019 01:51:47 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:
  docker: Use a stable snapshot for Debian Sid
  block/nvme: optimize the performance of nvme driver based on vfio-pci

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