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

Block layer patches

# gpg: Signature made Wed 18 Nov 2015 15:28:32 GMT using RSA key ID C88F2FD6
# gpg: Good signature from "Kevin Wolf <kwolf@redhat.com>"

* remotes/kevin/tags/for-upstream:
  block: Call external_snapshot_clean after blockdev-snapshot
  blockdev: Add missing bdrv_unref() in drive-backup
  iotests: fix race in 030
  nand: fix address overflow

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