NFSv4.1: Use the correct hostname in the client identifier string

We need to use the hostname of the process that created the nfs_client.
That hostname is now stored in the rpc_client->cl_nodename.

Also remove the utsname()->domainname component. There is no reason
to include the NIS/YP domainname in a client identifier string.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>