Fix VTS BatchingOperation Test.

Change list:
1. Cap minFifoCount to batching period worth of samples.
2. Modify the test period:
From :
batchingPeriodInNs * (0.8 + 0.8) = 1.6 times the batchingPeriodInNs
To
batchingPeriodInNs * (0.8 + 0.2) = batchingPeriodInNs

Bug: 185972775
Test: Verify pass by checking event count if it is closed to the
criteria.

Change-Id: Ied178150788e1a80d6fa6c87afbd1738ade48a0b