REP-946 Upgrade to Log4j 2.x

All of the tests need the `log4j-slf4j-impl` artifact to provide output anywhere other than the console. I will rescope the Log4J 2.x items to test in `repose-aggregator/pom.xml` and add them back to `repose-aggregator/core/valve/pom.xml` since that is the only one that actually utilizes it.