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

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

# gpg: Signature made Fri 14 Aug 2015 15:41:14 BST using RSA key ID 81AB73C8
# gpg: Good signature from "Stefan Hajnoczi <stefanha@redhat.com>"
# gpg:                 aka "Stefan Hajnoczi <stefanha@gmail.com>"

* remotes/stefanha/tags/block-pull-request:
  throttle: add throttle_max_is_missing_limit() test
  throttle: refuse bps_max/iops_max without bps/iops

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