Closing DOMXMLWriter will close System.out

Right now the constructor of DOMXMLWriter uses the default constructor of DOM4J's XMLWriter which uses System.out. Thus when we call close() on an instance of DOMXMLWriter we're closing System.out which isn't good.

This is what makes JUnit5's surefire provider fail in XCOMMONS-1189 (see https://github.com/junit-team/junit5/issues/801 for details).

Introduced in XWIKI-4627.