Use open_dir_by_path_walk in FSAL_LUSTRE lustre_lookup_path

Signed-off-by: Frank S. Filz <ffilzlnx@mindspring.com>
Don't allow ".." path elements in FSAL_PROXY pxy_lookup_path

symlink elements should result in errors, but we need to be explicit
about preventing use of ".." path elements in pxy_lookup_path.

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