Statsd pulls on-device power measurements

Pulls power rail measurements into statslog.

Bug: 119034725
Test: cts-tradefed run cts-dev -m CtsStatsdHostTestCases -t android.cts.statsd.atom.HostAtomTests
(after enabling OPTINAL_TESTS_ENABLED)

Change-Id: If083ae50160d508a9d180f748f9515557d35d8a1