Performance improvement

Performance improvement. [ZEPPELIN-86](https://zeppelin-project.atlassian.net/browse/ZEPPELIN-86)

Get new ruby script engine from script engine factory take very long time. 10~20 times/sec
Execution of query limited in this time.

This pull request re-use ruby script engine, so it eliminate script engine creation and finally get >200 Zql execution/sec.
All implementation and testcase included.