reretry ValueMetric implementation and pulling mechanism

Note:
This is for value metric. The default operations is sum the diffs.
The test uses kernel wake lock, which also needs dimension by kernel
wake lock name.

The test is a bit cumbersome as it needs StatsCompanionService to do
the alarm, which is not exact alarm.

The internal state of a slice of bucket would look something like this:

4:ipc0000005e_727_android.hardwar
0      0
4:SensorService_wakelock
40      64
4:ipc0000005c_727_android.hardwar
...

Test: manual test on device.
Change-Id: I2ed0ac7d3c5fcba8b7611d46f38a38ffd8bdc92a