pybind: use config values for timeout instead of RadosThread

RadosThread was introduced to implement timeouts in python level (http://tracker.ceph.com/issues/6507). Using config values are preferred as they are native to librados.
This change is somehow backward-incompatible but makes sense

Signed-off-by: Mohammad Salehe <salehe+dev@gmail.com>
pybind: code formatting and PEP8 fixes

Signed-off-by: Mohammad Salehe <salehe+dev@gmail.com>
pybind: Fix aio_read handling of string buffer

Read data may contain \0, and buf.value interprerts them as string terminator.

Signed-off-by: Mohammad Salehe <salehe+dev@gmail.com>