public String hostListAsString() {
    StringBuilder ret = new StringBuilder();
    if (this.hosts == null) {
      return "";
    }
    for (String host : this.hosts) {
      ret.append(host).append(":");
    }
    return ret.toString();
  }
Information that the API needs to provide to run bootstrap on hosts.
ambari-server/src/main/java/org/apache/ambari/server/bootstrap/SshHostInfo.java