rados.py: add some docstrings

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
rados.py: fix create_pool()

Call rados_pool_create_with_all() only if auid and crush_rule
are set properly. In case only crush_rule is set call
rados_pool_create_with_crush_rule() on librados, not the other
way around.

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
cephfs.py: add docstring for shutdown() and version()

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>