Include domain, IP address, and port in network error messages

[casey]

@atomgardner Is working on adding an announce subcommand in #466, which, since it interacts with the network, adds a new Network error type.

This error type should include the domain, IP address, and port of the remote host in the error message, to help users debug.

I'm opening this issue since doing this will be a bit of a headache, and I'd like to keep the initial PR as simple as possible.