safer srun termination #1705

Job	Run time
test-getting_started / tests	2m 5s
test-tutorials (configuration.ipynb) / tests	1m 28s
test-tutorials (debugging.ipynb) / tests	1m 46s
test-tutorials (describing_tasks.ipynb) / tests	2m 30s
test-tutorials (multiple_pilots.ipynb) / tests	3m 4s
test-tutorials (raptor.ipynb) / tests	2m 11s
test-tutorials (profiling.ipynb) / tests	2m 0s
test-tutorials (raptor_mpi.ipynb) / tests	4m 52s
test-tutorials (staging_data.ipynb) / tests	1m 54s
test-tutorials (submission.ipynb) / tests	1m 33s
	23m 23s

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