Fix some exception handling in nfs4.1

Some of the exception handling from the nfs4.0 version of nfs4lib was missing
from the nfs4.1 of nfs4lib.

Signed-off-by: Frank S. Filz <ffilzlnx@mindspring.com>
Fix problem in nfs4.1 if directory is empty

Signed-off-by: Frank S. Filz <ffilzlnx@mindspring.com>
4.1 server tests: fix cleanup

Server tests should clean up on exit.

Also, fix do_readdir so it doesn't bail out too soon on eof.

Signed-off-by: Frank S. Filz <ffilzlnx@mindspring.com>