Resync with xen-api-libs-specs

In particular we're now using ocaml-gnt for grant tables, we have
updated xcp-idl to include SR.probe and we have explicitly disabled
xenlight.

Signed-off-by: David Scott <dave.scott@citrix.com>
Merge pull request #403 from djs55/refresh-everything

Resync with xen-api-libs-specs