Write unit tests for directory_initiate_command_rend

To do this:

• Mock connection_connect to do nothing and return 0
• Mock directory_send_command to do nothing
• Mock connection_ap_make_link to return a fake connection
  • just return the partner connection that's passed to it?

It would be nice to get this done in 0.2.8, but I think it's more likely to be 0.2.9.