Call `shutdown' on exit. Add `on_timeout' and `on_expire' for `expired' and `timeouted' calls, do `stop' by default.

Signed-off-by: Anton D. Kachalov <mouse@yandex-team.ru>
Moveaway SnmpUdpClient to separate package python-fsmsnmp

Signed-off-by: Anton D. Kachalov <mouse@yandex-team.ru>