Running Spock tests in parallel

I ended up with the following issue on GitHub:

https://github.com/spockframework/spock/issues/691

Comment or whatever if you're also interested in parallel test execution in Spock.

In short, I've found a pull request with enabling parallel execution and it is even merged into one of the branches. However it is not merged into master yet. So the only way out I see for now is to write my own custom BaseSpecRunner