metric kairosdb.metric_counters is broken since 1.3.0

[sspieker]

After upgrading K* to version 1.3.0, the metric kairosdb.metric_counters indicated a massive drop of incoming metrics/datapoints: the number decreased from 13.6 billion to 5.9 billion.

We did not see any issues in dashboards, logs etc. that indicated any problems regarding metric ingestion.

But after digging through the commits between v1.2.2 and v1.3.0, we quickly spotted the cause: commit 06641c77352d415a3767b24eb1ed00d8240fe906 removed the host tag from this metric.
This makes kairosdb.metric_counters useless in all setups with more than one KairosDB instance (which I assume would be the majority).

I understand the reason for this change (high tag cardinality can be quite painful), but this solution should be reverted nonetheless as it makes the metric useless. In my opinion, there are other ways to make the (reverted) metric more accessable, i.e. by a scheduled aggregate or using the great new feature tag_indexed_row_key_lookup_metrics.