added scheduler capable to reconfigure tasks requirements #687

Job	Run time
test-getting_started / tests	2m 32s
test-tutorials (configuration.ipynb) / tests	1m 37s
test-tutorials (debugging.ipynb) / tests	2m 38s
test-tutorials (describing_tasks.ipynb) / tests	3m 42s
test-tutorials (multiple_pilots.ipynb) / tests	3m 20s
test-tutorials (profiling.ipynb) / tests	2m 38s
test-tutorials (raptor.ipynb) / tests	2m 34s
test-tutorials (raptor_mpi.ipynb) / tests	3m 42s
test-tutorials (staging_data.ipynb) / tests	2m 28s
test-tutorials (submission.ipynb) / tests	1m 33s
	26m 44s

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