IHealth: get* function return 0 on fail.

getChargeCounter, getCurrentNow, getCurrentAverage,
getCapacity, getEnergyCounter returns 0 when result is
not SUCCESS.

This is consistent with the invalid value defined
by @1.0::IHealthInfo and @2.0::IHealthInfo.
IHealthInfoCallback.healthInfoChanged() and
IHealth.getHealthInfo() both zero-fill invalid values.

This does not affect any clients, because client code
checks for result before using the value.

Test: health VTS test
Change-Id: I50e6faa5f4feb42bb1ec899e289567d6dde7e9c2