OAK-2315 Index cost is sometimes negative

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1643080 13f79535-47bb-0310-9956-ffa450edef68
OAK-1941 - rename RDB fixture for consistency

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1643084 13f79535-47bb-0310-9956-ffa450edef68