Merge remote-tracking branch 'remotes/ericb/tags/pull-nbd-2018-01-08' into staging

Merge remote-tracking branch 'remotes/ericb/tags/pull-nbd-2018-01-08' into staging

nbd patches for 2018-01-08

- Eric Blake: 0/2 Optimize sparse reads over NBD
- Murilo Opsfelder Araujo: block/nbd: fix segmentation fault when .desc is not null-terminated

# gpg: Signature made Mon 08 Jan 2018 15:21:19 GMT
# gpg:                using RSA key 0xA7A16B4A2527436A
# 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-2018-01-08:
  block/nbd: fix segmentation fault when .desc is not null-terminated
  nbd/server: Optimize final chunk of sparse read
  nbd/server: Implement sparse reads atop structured reply

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