Exposed some testAPIs in BatteryStatsManager

Added the following testsAPIs to replace the usage
of adb shell commands in tests:
* setChargerAcOnline
* setBatteryLevel
* unplugBattery
* resetBattery
* suspendBatteryInput

Test: atest MixedDeviceOwnerTest#testInstallUpdate using the adb
commands and the new testAPIs
Bug: 182260585

Change-Id: I48c2ad37f6240f4d7a3c437416fdcc0beeed6bd1