OAK-1099: node creation noticeably slower with mongoMk compared to tarMk
- adjust benchmark to better reflect the test case. the benchmark now only creates nodes and does not remove nodes anymore in the run method.

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1539273 13f79535-47bb-0310-9956-ffa450edef68