etcd: print initial cluster members during startup

etcd now prints the initial clusters members during startup.

```
2014/11/03 10:32:46 etcd: initial cluster members: etcd0=http://127.0.0.1:2380,etcd1=http://127.0.0.1:2390,etcd2=http://127.0.0.1:240
```
@kelseyhightower remove the "\n"? log.Printf adds a `\n`.