align metrics to 5min bundary

We use one alarm clock for all pulled atoms.
If metrics from different configs are not aligned,
the clock will be set to repeat at higher and higher
frequency, and consume a lot of battery.
Current implementation assumes a 5min minimum bucket
size. New metric start time is set to be aligned to
the start time of statsd in the next 5min.
So it will ignore events up to 5min.

align puller alarm to minute bundary

Test: unit test
Change-Id: I77ffa3c13de363c780b1000181b9a9b780dd0846