Merge remote-tracking branch 'remotes/ericb/tags/pull-nbd-2020-02-06' into staging

nbd patches for 2020-02-06

- Allow setting NBD description from QMP for parity with qemu-nbd
- Remove deprecated 'qemu-nbd --partition'

# gpg: Signature made Thu 06 Feb 2020 12:50:46 GMT
# gpg:                using RSA key 71C2CC22B1C4602927D2F3AAA7A16B4A2527436A
# 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-2020-02-06:
  qemu-nbd: Removed deprecated --partition option
  docs: Fix typo in qemu-nbd -P replacement
  nbd: Allow description when creating NBD blockdev

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