pnfs: GETDEVICELIST

The block driver uses GETDEVICELIST

Signed-off-by: Andy Adamson <andros@netapp.com>
[pass struct nfs_server * to getdevicelist]
[get machince creds for getdevicelist]
[fix getdevicelist decode sizing]
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: Benny Halevy <bhalevy@tonian.com>
Signed-off-by: Jim Rees <rees@umich.edu>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>