OAK-1845: Add command to execute script

Initial support for JavaScript file

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1596585 13f79535-47bb-0310-9956-ffa450edef68
OAK-1847: Use SegmentMK for testing where possible

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1596589 13f79535-47bb-0310-9956-ffa450edef68