Merge remote-tracking branch 'remotes/sstabellini/tags/cve-2015-5166-tag' into staging

cve-2015-5166

# gpg: Signature made Mon 03 Aug 2015 15:27:44 BST using RSA key ID 70E1AE90
# gpg: Good signature from "Stefano Stabellini <stefano.stabellini@eu.citrix.com>"

* remotes/sstabellini/tags/cve-2015-5166-tag:
  Fix release_drive on unplugged devices (pci_piix3_xen_ide_unplug)

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