Merge remote-tracking branch 'remotes/ericb/tags/pull-nbd-2018-07-02' into staging

Merge remote-tracking branch 'remotes/ericb/tags/pull-nbd-2018-07-02' into staging

nbd patches for 2018-07-02

Bug fixes and iotest exposure of fleecing via NBD (serving a
read-only point-in-time view via blockdev-backup sync:none,
as well as serving dirty bitmaps over NBD), including a new
x-dirty-bitmap parameter when opening NBD clients as the
counterpart to x-nbd-server-add-bitmap. Also a random fix
for iscsi block_status spotted by Coverity that missed other
miscellaneous trees.

- Eric Blake: nbd/server: Fix dirty bitmap logic regression
- Eric Blake: iscsi: Avoid potential for get_status overflow
- John Snow/Vladimir Sementsov-Ogievskiy: 0/2 block: formalize and test fleecing
- Eric Blake: 0/2 test NBD bitmap export

# gpg: Signature made Tue 03 Jul 2018 02:33:03 BST
# 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-2018-07-02:
  iotests: New test 223 for exporting dirty bitmap over NBD
  nbd/client: Add x-dirty-bitmap to query bitmap from server
  iotests: add 222 to test basic fleecing
  blockdev: enable non-root nodes for backup source
  iscsi: Avoid potential for get_status overflow
  nbd/server: Fix dirty bitmap logic regression

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