Return a file layout instead of device. This will allow
to return different layout types and striping patters
depending on NFSv41DeviceManager implementations.

Match method names to NFS spec. This makes current code
incompatible with any existing implementations
( dCache is the only one which I aware about :) )
The NFSv4Client is included into NFSv41DeviceManager calls
to enable behavior change depending on client.

Acked-By: Gerd
Patch: http://rb.dcache.org/r/1753/