GROOVY-6081: Improve unit tests execution time (Part 2)

https://jira.codehaus.org/browse/GROOVY-6081
GROOVY-6081: Improve unit tests execution time

With the decreased sleep time the test does not succeed every time on the build server, therefore I increased the sleep time a bit.
Test still fails sometimes on the build sever, going back to the old "slow" version