Update ax_multiobjective_nas_tutorial.py to use TensorboardMetric #2619

Job	Run time
pytorch_tutorial_build_worker (1, 15, linux.g5.12xlarge.nvidia.gpu)	17m 30s
pytorch_tutorial_build_worker (2, 15, linux.g5.4xlarge.nvidia.gpu)	54m 13s
pytorch_tutorial_build_worker (3, 15, linux.g5.4xlarge.nvidia.gpu)	21m 45s
pytorch_tutorial_build_worker (4, 15, linux.g5.4xlarge.nvidia.gpu)	30m 17s
pytorch_tutorial_build_worker (5, 15, linux.g5.4xlarge.nvidia.gpu)	22m 37s
pytorch_tutorial_build_worker (6, 15, linux.g5.4xlarge.nvidia.gpu)	19m 58s
pytorch_tutorial_build_worker (7, 15, linux.4xlarge.nvidia.gpu)	25m 46s
pytorch_tutorial_build_worker (8, 15, linux.4xlarge.nvidia.gpu)	24m 41s
pytorch_tutorial_build_worker (9, 15, linux.4xlarge.nvidia.gpu)	41m 46s
pytorch_tutorial_build_worker (10, 15, linux.4xlarge.nvidia.gpu)	46m 56s
pytorch_tutorial_build_worker (11, 15, linux.4xlarge.nvidia.gpu)	38m 39s
pytorch_tutorial_build_worker (12, 15, linux.4xlarge.nvidia.gpu)	23m 55s
pytorch_tutorial_build_worker (13, 15, linux.4xlarge.nvidia.gpu)	27m 50s
pytorch_tutorial_build_worker (14, 15, linux.4xlarge.nvidia.gpu)	19m 41s
pytorch_tutorial_build_worker (15, 15, linux.4xlarge.nvidia.gpu)	29m 16s
pytorch_tutorial_build_manager	21m 36s
	7h 46m 26s

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