health 2.1 VTS: fix test on batteryFullCapacityUah

getHealthInfo_2_1 reports batteryFullCapacityUah:
- 0 if value is unknown. In such case, no requirement is enforced.
- positive if value is known. In such case, require it to be 50%~120% of
  batteryFullCharge.

Test: run on cuttlefish
Bug: 144948996

Change-Id: I7856729aafa3a19a3bfcc00e6e0ad5162f22afea