Merge remote-tracking branch 'remotes/cohuck/tags/s390x-20150714' into staging

s390x fixes for 2.4:
- virtio migration regression
- missing diag288 watchdog resets

# gpg: Signature made Tue Jul 14 18:17:54 2015 BST using RSA key ID C6F02FAF
# gpg: Good signature from "Cornelia Huck <huckc@linux.vnet.ibm.com>"
# gpg:                 aka "Cornelia Huck <cornelia.huck@de.ibm.com>"

* remotes/cohuck/tags/s390x-20150714:
  s390/virtio-ccw: Fix migration
  watchdog/diag288: correctly register for system reset requests

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