Merge remote-tracking branch 'remotes/armbru/tags/pull-block-2017-03-28' into staging

Block patches for 2017-03-28

# gpg: Signature made Tue 28 Mar 2017 14:41:37 BST
# gpg:                using RSA key 0x3870B400EB918653
# gpg: Good signature from "Markus Armbruster <[email protected]>"
# gpg:                 aka "Markus Armbruster <[email protected]>"
# Primary key fingerprint: 354B C8B3 D7EB 2A6B 6867  4E5F 3870 B400 EB91 8653

* remotes/armbru/tags/pull-block-2017-03-28:
  block: Declare blockdev-add and blockdev-del supported

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