Allows the CLI to skip some tests, for example: mvn test -Dlog4j.skip.test1=**/ConfigurationTest.java -Dlog4j.skip.test2=**/FileOutputTest.java

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1583524 13f79535-47bb-0310-9956-ffa450edef68