pybind: Some fixes on semantics

This was primarily added to let signals like SIGINT generated by ^C be handled by python, instead of being hidden from it while the main thread was running librados code. It was added when the ceph command line tool was rewritten in python and to use librados, so that you could still kill the ceph command at any time.

The timeout handling (just used by the *_command() and connect() functions) is a bit redundant now though.
It'd be nice to make ceph.in set the new rados config timeout parameters instead, but there's not really a good way to handle them separately for each *_command() function without race conditions, so for backwards compatibility I'd rather keep RadosThread and the calls to it as they are in rados.py.