Merge remote-tracking branch 'remotes/ericb/tags/pull-nbd-2017-10-30' into staging

Merge remote-tracking branch 'remotes/ericb/tags/pull-nbd-2017-10-30' into staging

nbd patches for 2017-10-30

Vladimir Sementsov-Ogievskiy (some patches co-authored by Eric Blake):
00/12 nbd minimal structured read

# gpg: Signature made Mon 30 Oct 2017 20:54:54 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-2017-10-30:
  nbd: Minimal structured read for client
  nbd: Move nbd_read() to common header
  nbd/client: prepare nbd_receive_reply for structured reply
  nbd/client: refactor nbd_receive_starttls
  nbd/server: Include human-readable message in structured errors
  nbd: Minimal structured read for server
  nbd/server: Refactor zero-length option check
  nbd/server: Simplify nbd_negotiate_options loop
  nbd/server: Report error for write to read-only export
  nbd: Expose constants and structs for structured read
  nbd: Move nbd_errno_to_system_errno() to public header
  nbd: Include error names in trace messages

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