refactor(etcd): Init etcd client before registry.New
feat(etcd): Define EtcdServers in coreinit config
feat(etcd): Add --endpoint flag to corectl

The --endpoint flag allows a custom API endpoint to be used. The coreinit
API endpoint is just etcd.
Merge pull request #39 from bcwaldon/etcd-server

Configure etcd server coreinit and corectl should hit
refactor(machine): Store mach object as state in place of addrs
refactor(config): Move default bootid into machine.New
refactor(machine): Drop dead ip-related code
refactor(machine): Publish public_ip from config file with machine
refactor(socket): Replace socket address with machine.PublicIP