OAK-1847: Use SegmentMK for testing where possible

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1596603 13f79535-47bb-0310-9956-ffa450edef68
doc: Some SegmentMK doc updates

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1596609 13f79535-47bb-0310-9956-ffa450edef68