added scheduler capable to reconfigure tasks requirements #731

Job	Run time
test-getting_started / tests	2m 41s
test-tutorials (configuration.ipynb) / tests	1m 45s
test-tutorials (debugging.ipynb) / tests	2m 17s
test-tutorials (describing_tasks.ipynb) / tests	3m 14s
test-tutorials (multiple_pilots.ipynb) / tests	11m 30s
test-tutorials (profiling.ipynb) / tests	2m 19s
test-tutorials (raptor.ipynb) / tests	2m 19s
test-tutorials (raptor_mpi.ipynb) / tests	3m 57s
test-tutorials (staging_data.ipynb) / tests	2m 19s
test-tutorials (submission.ipynb) / tests	1m 25s
	33m 46s

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