This diff adds to miniooni support for using the torsf tunnel. Such a tunnel consists of a snowflake pluggable transport in front of a custom instance of tor and requires tor to be installed. The usage is like: ``` ./miniooni --tunnel=torsf [...] ``` The default snowflake rendezvous method is "domain_fronting". You can select the AMP cache instead using "amp": ``` ./miniooni --snowflake-rendezvous=amp --tunnel=torsf [...] ``` Part of https://github.com/ooni/probe/issues/1955