[MJAR-162] skipIfEmpty not work for test-jar goal and empty directories

git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/trunk@1444045 13f79535-47bb-0310-9956-ffa450edef68
git doesn't like empty directories

git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/trunk@1444046 13f79535-47bb-0310-9956-ffa450edef68