fix JUnit reports style directory for forked execution
rework default configuration for all the forked modes
start background JVM for running tests when interactive mode starts, avoiding initial startup costs for running tests
Merge branch 'master' of github.com:grails/grails-core
Revert "upgrade to Groovy 2.1.0 final"

This reverts commit 05ea23cddf762e96f7af3c97b6d7bad5d26253c3.