Import changeset 386:b03b9dc4f68b from XenServer's xen-4.4.pq.hg

Original commit message:

    CP-8777 - Allow Xapi to query whether xenguest read/writes a legacy stream or a v2 stream

Authored-by: Andrew Cooper <andrew.cooper3@citrix.com>
Imported-by: Si Beaumont <simon.beaumont@citrix.com>