Endpoint selection strategy based on peer ID

[thanethomson]

Right now, tm-load-test selects endpoints based on IP address, but in some cases the same node may have two different IP addresses (e.g. one might configure an endpoint as 127.0.0.1, but pick up the same node through crawling the network by way of its public IP address, and tm-load-test cannot tell they're the same node).

A better strategy for endpoint selection would be to do so by way of peer ID.