Remove assumptions about peer ports

[swsnider]

Per a discussion (https://groups.google.com/d/msgid/prometheus-developers/CAL%2BpMaAC4mo%3DaD1D7PbUcK1S0UAQ2YqyzhE%2BjND7tt_8ys0MtQ%40mail.gmail.com?utm_medium=email&utm_source=footer) on the Prometheus mailing list about the component that uses this mesh library, it appears that if a peer's port is not the same as one of the ports in the statically configured initial peers list, the other cluster members will fail to connect to it directly, presumably because the gossip messages about peer membership don't contain port information.

I have a use case where I run software on top of a cluster scheduler (like Apache Aurora) where I get random assigned ports for each instance in there cluster, which would mean that I can't use anything that uses this library in that cluster effectively. Please fix the library so that there are no hidden assumptions about how to connect to each peer.