Add import os to example code block (#3378) #4499

Job	Run time
pytorch_tutorial_build_worker (1, 15, linux.g5.12xlarge.nvidia.gpu)	16m 13s
pytorch_tutorial_build_worker (2, 15, linux.g5.4xlarge.nvidia.gpu)	39m 51s
pytorch_tutorial_build_worker (3, 15, linux.g5.4xlarge.nvidia.gpu)	22m 3s
pytorch_tutorial_build_worker (5, 15, linux.g5.4xlarge.nvidia.gpu)	23m 23s
pytorch_tutorial_build_worker (8, 15, linux.g5.4xlarge.nvidia.gpu)	22m 15s
pytorch_tutorial_build_worker (9, 15, linux.g5.4xlarge.nvidia.gpu)	19m 3s
pytorch_tutorial_build_worker (4, 15, linux.g5.4xlarge.nvidia.gpu)	36m 59s
pytorch_tutorial_build_worker (12, 15, linux.g5.4xlarge.nvidia.gpu)	20m 52s
pytorch_tutorial_build_worker (14, 15, linux.g5.4xlarge.nvidia.gpu)	26m 21s
pytorch_tutorial_build_worker (10, 15, linux.g5.4xlarge.nvidia.gpu)	16m 23s
pytorch_tutorial_build_worker (11, 15, linux.g5.4xlarge.nvidia.gpu)	15m 27s
pytorch_tutorial_build_worker (13, 15, linux.g5.4xlarge.nvidia.gpu)	30m 20s
pytorch_tutorial_build_worker (6, 15, linux.g5.4xlarge.nvidia.gpu)	22m 37s
pytorch_tutorial_build_worker (15, 15, linux.g5.4xlarge.nvidia.gpu)	31m 57s
pytorch_tutorial_build_worker (7, 15, linux.g5.4xlarge.nvidia.gpu)	19m 34s
pytorch_tutorial_build_manager	23m 26s
	6h 26m 44s

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