Split 2 of the initial submission
pgbench: reduce and compensate throttling underestimation bias.
This is a consequence of relying on an integer random generator,which allow to ensure that delays inserted stay reasonably inrange of the target average delay.
The bias was about 0.5% with 1000 distinct values. Multiplier addedto compensate the 0.05% bias with 10000 distinct integer values,so there is no bias now.