Releasing interpreter resources after the schedule job.

[Hyung Sung Shim]

Hello devs.

Zeppelin notebook scheduler is awsome functionality but the resource of
interpreter does not release even if schedule job has ended.

Maybe sometimes user want to release resource when end of schedule,
so how about adding function to release the interpreter resources after
schedule job as user option?

If you think need this, i would like to contribute.
Please feel free to share your opinion.

Thanks.