Make query_range more robust.

Gracefully handle decimal values, by truncating them.

Limit amount of steps, to avoid accidentally pulling too much data.
This limit returns up to ~500kB per timeseries, and allows
for 60s granularity for a week and 1h granularity for a year.

Change-Id: Ie549fc24deb2eecbc6c5d1b6088a548a6b02e849