Merge remote-tracking branch 'remotes/cody/tags/block-pull-request' into staging

# gpg: Signature made Fri 24 Feb 2017 17:45:53 GMT
# gpg:                using RSA key 0xBDBE7B27C0DE3057
# gpg: Good signature from "Jeffrey Cody <[email protected]>"
# gpg:                 aka "Jeffrey Cody <[email protected]>"
# gpg:                 aka "Jeffrey Cody <[email protected]>"
# Primary key fingerprint: 9957 4B4D 3474 90E7 9D98  D624 BDBE 7B27 C0DE 3057

* remotes/cody/tags/block-pull-request:
  RBD: Add support readv,writev for rbd
  block/nfs: try to avoid the bounce buffer in pwritev
  block/nfs: convert to preadv / pwritev

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