obfsproxy does not handle SIGINTs as the pt-spec wants
From the pt-spec:
Proxies should respond to a single INT signal by closing their listener ports and not accepting any new connections, but keeping all connections open, then terminating when connections are all closed. Proxies should respond to a second INT signal by shutting down cleanly.
We used to do this in C-obfsproxy, but we are not doing it in the current Python codebase.
If we still believe it's a good idea, we should implement it in obfsproxy again.