Update flake8 configuration #496

Job	Run time
Test aip-encrypt on Firefox	28m 58s
Test aip-encrypt on Chrome	29m 29s
Test aip-encrypt-mirror on Firefox	17m 30s
Test aip-encrypt-mirror on Chrome	23m 42s
Test black-box on Chrome	40m 27s
Test icc on Firefox	20m 8s
Test icc on Chrome	18m 51s
Test ipc preservation on Firefox	24m 44s
Test ipc preservation on Chrome	24m 16s
Test ipc access on Firefox	24m 34s
Test ipc access on Chrome	22m 58s
Test metadata-xml on Firefox	29m 39s
Test metadata-xml on Chrome	25m 27s
Test tcc on Firefox	18m 24s
Test tcc on Chrome	17m 49s
Test tpc on Firefox	18m 56s
Test tpc on Chrome	19m 16s
Test uuids-dirs on Firefox	19m 14s
Test uuids-dirs on Chrome	18m 25s
	7h 22m 47s

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