SLING-3037 : IllegalArgumentException in logback Logger. Revert

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1520517 13f79535-47bb-0310-9956-ffa450edef68
SLING-3037 : IllegalArgumentException in logback Logger. Apply patch from Chetan Mehrotra 

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1520518 13f79535-47bb-0310-9956-ffa450edef68