pybind/ceph_argparse: avoid int overflow

pybind/ceph_argparse: avoid int overflow

in python 2.6.8, `thread.join(timeout)` tries to convert the given
timeout to PyTime, but turns out `2 << 32` overflows when python
runtime converts the timeout from sec to ns. that's why
the `lock.acquire()` call always fail in
`Thread._wait_for_tstate_lock()`.
and we end up with an alive thread after calling `thread.join()`.

Signed-off-by: Kefu Chai <kchai@redhat.com>