Relieve Sensor Event Gap Test Criterion

* Change the tolerance percentage from 1% to 2%. The maximum is increase
  proportionally as well.
* Fix the tolerance calculation, avoid rounding error.
* Minor change of code FifoLengthVerification and SensorBatching
  FifoTest. Code logic kept unchanged.

Bug: b/24680993

Change-Id: I376bc5a8351c95e8230a61f2749288efc50257f2
3 files changed