Merge remote-tracking branch 'remotes/ericb/tags/pull-nbd-2018-04-02' into staging

Merge remote-tracking branch 'remotes/ericb/tags/pull-nbd-2018-04-02' into staging

nbd patches for 2018-04-02

- Eric Blake: nbd: Fix 32-bit compilation on BLOCK_STATUS
- Eric Blake: nbd/client: Correctly handle bad server REP_META_CONTEXT
- Eric Blake: nbd: trace meta context negotiation

# gpg: Signature made Mon 02 Apr 2018 15:15:01 BST
# gpg:                using RSA key A7A16B4A2527436A
# gpg: Good signature from "Eric Blake <eblake@redhat.com>"
# gpg:                 aka "Eric Blake (Free Software Programmer) <ebb9@byu.net>"
# gpg:                 aka "[jpeg image of size 6874]"
# Primary key fingerprint: 71C2 CC22 B1C4 6029 27D2  F3AA A7A1 6B4A 2527 436A

* remotes/ericb/tags/pull-nbd-2018-04-02:
  nbd: trace meta context negotiation
  nbd/client: Correctly handle bad server REP_META_CONTEXT
  nbd: Fix 32-bit compilation on BLOCK_STATUS

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