Consider using getifaddrs for _find_myself

[jfriesse]

Current _find_myself function is using netlink and that's not very portable and as https://github.com/ClusterLabs/booth/pull/139 shows it can "change". Idea is to migrate _find_myself function to use getifaddrs which seems to be more stable and also better portable (not really needed because booth is Linux only, but still might be nice to have)