Merge remote-tracking branch 'remotes/ericb/tags/pull-nbd-2019-05-07' into staging

nbd patches for 2019-05-07

- iotest improvements

# gpg: Signature made Tue 07 May 2019 16:00:18 BST
# gpg:                using RSA key A7A16B4A2527436A
# gpg: Good signature from "Eric Blake <eblake@redhat.com>" [full]
# gpg:                 aka "Eric Blake (Free Software Programmer) <ebb9@byu.net>" [full]
# gpg:                 aka "[jpeg image of size 6874]" [full]
# Primary key fingerprint: 71C2 CC22 B1C4 6029 27D2  F3AA A7A1 6B4A 2527 436A

* remotes/ericb/tags/pull-nbd-2019-05-07:
  iotests: Make 182 do without device_add
  iotests: Tweak 221 sizing for different hole granularities
  tests/qemu-iotests: Fix more reference output files due to recent qemu-io change
  iotests: Fix 233 for ports other than 10809
  qemu-nbd: Look up flag names in array

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