Fix off by one error in timestamp jitter calculation

getPercentileValue returns floor of the actual index. In cases of
very low number of events is being collected, there may be no outlier
event being dropped which can result in a test failure on
implementation that met spec.

This CL revisited the getPercentileValue function and addresses this
edge case.

Test: Outliers are correctly dropped in sensor tests of various rate.
Change-Id: I53a981e78adf793f7f154d05d88083c58cc30fd2
2 files changed