Merge remote-tracking branch 'remotes/ericb/tags/pull-nbd-2018-10-03-v2' into staging

Merge remote-tracking branch 'remotes/ericb/tags/pull-nbd-2018-10-03-v2' into staging

nbd patches for 2018-10-03

Fix bugs in NBD_CMD_CACHE, drop support for oldstyle NBD server,
minor build and doc fixes

- Denis V. Lunev: nbd: fix NBD_CMD_CACHE negitiation... [retitled]
- Vladimir Sementsov-Ogievskiy: 0/2 server: drop old-style negotiation
- Eric Blake: qemu-nbd: Document --tls-creds
- Vladimir Sementsov-Ogievskiy: nbd/server: fix NBD_CMD_CACHE
- Peter Maydell: nbd: Don't take address of fields in packed structs

# gpg: Signature made Thu 04 Oct 2018 15:19:32 BST
# gpg:                using RSA key A7A16B4A2527436A
# gpg: Good signature from "Eric Blake <[email protected]>"
# gpg:                 aka "Eric Blake (Free Software Programmer) <[email protected]>"
# 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-2018-10-03-v2:
  nbd: fix NBD_FLAG_SEND_CACHE value
  nbd/server: drop old-style negotiation
  qemu-nbd: drop old-style negotiation
  qemu-nbd: Document --tls-creds
  nbd/server: fix NBD_CMD_CACHE
  nbd: Don't take address of fields in packed structs

Signed-off-by: Peter Maydell <[email protected]>