OAK-1528 - Update Slf4j Api dependency to 1.7.6

Modifying the paxexam setup to use latest Pax Logging which exports 1.7.x version of Slf4j API bundle

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1577026 13f79535-47bb-0310-9956-ffa450edef68