Various TrigValSteering test improvements
This is a collection of several small improvements for trigger ART test scripts based on TrigValSteering (ATR-20038).
Each change is a separate commit:
- Fix RegTest reference handling and TrigP1Test regex
- Add art createpoolfile pre-exec for grid tests
- Fix log zip step
- Skip ZeroCounts check for EmptyMenu tests
- Describe dry run option in README
- Add unit tests of ART test scripts