Test files incorrectly handled by GroovySourceImporter
sonar-cobertura-plugin should be reusable
Seems that cobertura-maven-plugin 2.2 doesn't work for Groovy.
Implemented in r2228, but it's dirty implementation, because contains big part of sonar-cobertura-plugin - see SONAR-1808.
Integration tests updated in r2272 - generates a lot of noise during build due to debug output from tests, but works.