pybind/cephfs:  Cleanups to cephfs pybind

Cleanups proposed by jdurgin:
https://github.com/ceph/ceph/commit/67df49bf3d644ff7c2996eb1f27fed333bade64a#commitcomment-2671141

Signed-off-by: Sam Lang <sam.lang@inktank.com>
qa/workunits/restart: Fix arg check ordering

Signed-off-by: Sam Lang <sam.lang@inktank.com>