Reduce the chance of BatteryStats background work affecting CTS tests

Add some utility methods to help get consistent behavior from
batterystats

Fixes: 185970842
Test: atest android.cts.statsdatom.statsd.HostAtomTests#testPluggedStateChangedAtom --rerun-until-failure
Test atest
android.cts.statsdatom.statsd.HostAtomTests#testBatterySaverModeStateChangedAtom
--rerun-until-failure
Change-Id: Ic1946cb3adc00135d6a510e12de368ee3f2988e1

Change-Id: I3a340a1316a5d11bd88b31345b3b06f70f67289a
2 files changed