* Prometheus: Fix actual step computation logic when a min_step is specified and the range is longer than min_step * 11000.

* Fix kbn.round_interval for exact intervals.

* Remove redundant 1d return, fix a couple of comments.

* Be more cautious with values close to 1d not rounding up to 1d. They may, because of the way the calculation uses 2 potentially different current time values.