change defaults for Dropout and BatchNorm #4270

Job	Run time
Build tunix package / Build Tunix wheel	9s
tunix_cpu_unit_tests / run	1m 24s
tunix_tpu_unit_tests / run_dev	22m 48s
tunix_tpu_unit_tests / run_prod	12m 17s
Notify failed build	3s
	36m 41s

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