Min is missing in Histogram

[LotharSee]

The current Histogram doesn't report min (but does avg/max/median/count/95percentile).
It does impact both Agent checks and DogStatsD.

It is a one-line change to add it.

https://github.com/DataDog/dd-agent/blob/master/aggregator.py#L243

[remh]

Should be pretty straight forward but it will automatically increase the number of histogram metrics by 20%.

I'll check that with the metrics team.

[remh]

Fixed by #1303