TESTS: Add test for future interrupting itself; some backends ignore it #474

Job	Run time
future.plan=cluster	2m 31s
future.plan=multicore	1m 51s
future.plan=multisession	3m 17s
future.plan=sequential	2m 16s
future.plan=future.batchtools::batchtools_local	3m 51s
future.plan=future.batchtools::batchtools_bash	4m 35s
future.plan=future.callr::callr	2m 29s
future.plan=future.mirai::mirai_multisession	1m 48s
future.plan=future.mirai::mirai_cluster	2m 45s
	25m 23s

Provide feedback