SLING-3017 improve Karaf integration tests

- separate testing support and test into own packages and jars
- use Maven Failsafe Plugin for tests
- update Pax Exam to 3.2.0
- enable test (remove Ignore annotation)
- increase timeouts to 300000 ms

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1528821 13f79535-47bb-0310-9956-ffa450edef68