job_coordinator: terminate a job if there is a scheduling failure in new_task.

This commit should resolve issue #553.
The kind of scheduling failures that arise from calling new_task are not
recoverable.

The job_coordinator cannot simply retry the failed task because it does not have
enough information about whether the previous submission was successful or not.
Merge pull request #559 from pooya/558

job_coordinator: terminate a job if there is a scheduling failure in new_task.

This closes issue #558