This adds tor-related CLI arguments to "create-node" and
"create-introducer", to control exactly how we should be using Tor.
* --tor-launch
* --tor-executable=
* --tor-control-port=
I went with "--tor-launch" instead of "--launch-tor" for consistency. I
don't particularly like the grammatical flow of it, and it doesn't
actually put all the tor-related arguments next to each other in the
--help output (the flags are put in one block, then the parameters in
the next). But it seems slightly more consistent to start all the
tor-related argument names with a "--tor*" prefix.