Merge remote-tracking branch 'remotes/sstabellini/tags/xen-20160905' into staging

Xen 2016/09/05

# gpg: Signature made Mon 05 Sep 2016 19:59:47 BST
# gpg:                using RSA key 0x894F8F4870E1AE90
# gpg: Good signature from "Stefano Stabellini <stefano.stabellini@eu.citrix.com>"
# Primary key fingerprint: D04E 33AB A51F 67BA 07D3  0AEA 894F 8F48 70E1 AE90

* remotes/sstabellini/tags/xen-20160905:
  xen: use native disk xenbus protocol if possible

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