Time zones do not shift correctly from normal to DST with GROUP BY time(2h)

[jsternberg]

Bug report

System info: InfluxDB 1.3.1

Steps to reproduce:

1. Insert some data around the shift from normal to DST.
2. Query using a grouping that causes one of the buckets to fall exactly on the switch.

The easiest way to do step 2 is to use GROUP BY time(2h) since the DST switch happens at 2 AM in the US. In other time zones where the boundary may fall on a different area, other groupings may pop up as problems.

This also does not appear to happen when the bucket does not land directly on the edge between time zones. So a grouping of 1d ends up being fine and was the primary mode that this was tested against.

Expected behavior: When losing an hour, the time advances from 2:00 AM to 3:00 AM. I expect the interval starting at 12:00 AM to go to 3:00 AM (since 2 AM advances to 3 AM immediately) and I expect the 2 AM interval to go from 3 AM to 4 AM.

Actual behavior: The 12:00 AM interval goes from 12:00 AM to 1:00 AM and the 2:00 AM interval goes from 1:00 AM to 3:00 AM.