Use `-peers` in `etcdctl members` commands

This is still incredibly stupid, but it gets us far enough for v0.5.0-alpha.1. It only uses the first argument to `-peers` without any retries, but the framework is there to introduce the retry logic ASAP. I plan to continue improving this immediately.
sure, but then the host will not get prefixed with a scheme if it is httparty.example.com