storaged: exit if batteryproperties service is dead.

storaged relies on batteryproperties service (healthd) to provide
charger stats. If healthd is killed, kill storaged as well. Both
will be restarted by init process anyway to restore a correct state.

Test: kill healthd when storaged is running
Bug: 36652060
Change-Id: Ia785bb6f5ea259aa43cd1efab9505ebefaf3db12