Merge remote-tracking branch 'remotes/kevin/tags/for-upstream' into staging

Block layer patches

# gpg: Signature made Wed 02 Dec 2015 15:57:35 GMT using RSA key ID C88F2FD6
# gpg: Good signature from "Kevin Wolf <kwolf@redhat.com>"

* remotes/kevin/tags/for-upstream:
  blkdebug: silence warning under qtest
  qcow2: Fix potential qemu-img check crash on 32 bit hosts

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