SLING-3049 - Make Logback Stacktrace Packaging data support OSGi aware

Making the assertion in testcase more precise

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1542896 13f79535-47bb-0310-9956-ffa450edef68
SLING-2024 - Replace file logger with logback

In preparation for release. Minor cleanups

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1542897 13f79535-47bb-0310-9956-ffa450edef68