fix ./flow nodeindex:cleanup command

MERGE: fix nodeindex:cleanup command in Elasticsearch >= 2.x

In the cleanup command there was a regression introduced with 314ecac2cb88055b724943e9ad96bb6fb10f1cac where it tried to log an object.

In ESv2 /_status was removed in favor of /_stats (see https://www.elastic.co/guide/en/elasticsearch/reference/2.0/breaking_20_stats_info_and_literal_cat_literal_changes.html#_index_status_api and https://www.elastic.co/guide/en/elasticsearch/reference/2.0/indices-status.html).