Previously, DataValidator would automatically reject sensor data as
stale if (almost) constant.
But if setting SIH_NOISE_SCALE = 0 for deterministic sim, constant
sensor data are to be expected.
This adds logic to not flag sensor values as stale if noise scale is
very small. If the sensor has *actually* gone stale with very low noise
scale, this means we cannot detect it anymore.
Balduin
5c08b11442