Randomness in the validator

[ml-evs]

From discussion with @markus1978

[markus1978]

A parameter that allows to fix formulas, queries, ids that are usually taken from the first page of results would allow to make the validator outcome deterministic.

On the other extreme, if the validator could go through many randomly selected pages, entries, queries for a long time, we could use this to find lots of otherwise hard to find error states.

[merkys]

This could be fixed by introducing a command line parameter to set a fixed seed for randomization. I see the use of reproducible validator runs.