safer srun termination #1698

Job	Run time
test-getting_started / tests	1m 53s
test-tutorials (configuration.ipynb) / tests	1m 24s
test-tutorials (debugging.ipynb) / tests	2m 2s
test-tutorials (describing_tasks.ipynb) / tests	2m 55s
test-tutorials (profiling.ipynb) / tests	2m 19s
test-tutorials (raptor.ipynb) / tests	2m 22s
test-tutorials (multiple_pilots.ipynb) / tests	2m 46s
test-tutorials (raptor_mpi.ipynb) / tests	3m 11s
test-tutorials (submission.ipynb) / tests	1m 25s
test-tutorials (staging_data.ipynb) / tests	2m 7s
	22m 24s

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