fix(etcd): fixup the name and data dir guessing

- Only generate the name from a hostname if the data dir is not
  specified and the name is not specified

- Only guess the data dir from Name if the data dir wasn't already
  specified
Merge pull request #341 from philips/fixup-name-and-data-dir-guessing

fix(etcd): fixup the name and data dir guessing
fix(README): link to etcdctl directly

link to the etcdctl homepage directly
Merge branch 'master' of https://github.com/coreos/etcd into mod-lock
Fix test harness.