Volume.clone: the primary key should be the filename, not URI
Volume.clone: the primary key should be the filename, not URI

To discover the URIs, the client performs a Volume.stat providing the
key. The client then calls Datapath.attach with a URI from Volume.stat.

Signed-off-by: David Scott <63c9eb0ea83039690fefa11afe17873ba8278a56@eu.citrix.com>

franciozzy/ffs,robertbreker/ffs,xapi-project/ffs,djs55/ffs