Merge remote-tracking branch 'remotes/ericb/tags/pull-nbd-2018-03-01' into staging

nbd patches for 2018-03-01

- Eric Blake: nbd: Honor server's advertised minimum block size
- Vladimir Sementsov-Ogievskiy: partial: nbd block status base:allocation

# gpg: Signature made Thu 01 Mar 2018 21:01:22 GMT
# 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-2018-03-01:
  nbd/client: fix error messages in nbd_handle_reply_err
  nbd: BLOCK_STATUS constants
  nbd: change indenting in nbd.h
  nbd: Honor server's advertised minimum block size

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