Remove the WARNING during integration tests

notice one WARNING:
[INFO] Building: non-default-config-headerfiles/pom.xml
[INFO] run post-build script verify.groovy
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by org.codehaus.groovy.reflection.CachedClass 
(file:/.m2/repository/org/codehaus/groovy/groovy-all/2.4.8/groovy-
all-2.4.8.jar) to method java.lang.Object.finalize()
WARNING: Please consider reporting this to the maintainers of 
org.codehaus.groovy.reflection.CachedClass
WARNING: Use --illegal-access=warn to enable warnings of further illegal 
reflective access operations
WARNING: All illegal access operations will be denied in a future release
[INFO]           non-default-config-headerfiles/pom.xml ........... SUCCESS (2.4 
s)