Use a default configuration for the oak fixture in launchpad/testing

This will be picked up by both runmodes ( jackrabbit and oak ) but in
practice there is no side-effect and the config does not seem to be
picked up if I place it under src/main/config/oak.

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1630233 13f79535-47bb-0310-9956-ffa450edef68