OAK-641: Improved benchmark tooling

Document how to add new benchmarks

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1526222 13f79535-47bb-0310-9956-ffa450edef68
OAK-641: Improved benchmark tooling

Prevent Derby from polluting the current directory with log files

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1526223 13f79535-47bb-0310-9956-ffa450edef68