RL Deepracer Notebook FileNotFoundError

In: https://github.com/awslabs/amazon-sagemaker-examples/blob/master/reinforcement_learning/rl_deepracer_robomaker_coach_gazebo/deepracer_rl.ipynb

Notebook fails when retrieving: training_metrics.json
`FileNotFoundError: S3 object s3://.../training_metrics.json never appeared after 1200 seconds`

Occurs when you run:
`training_metrics_file = "training_metrics.json" `
`training_metrics_path = "{}/{}".format(s3_prefix, training_metrics_file)`
`wait_for_s3_object(s3_bucket, training_metrics_path, tmp_dir)`

To reproduce error:

Launch SM Notebook instance
Clone https://github.com/awslabs/amazon-sagemaker-examples.git
Open https://github.com/awslabs/amazon-sagemaker-examples/blob/master/reinforcement_learning/rl_deepracer_robomaker_coach_gazebo/deepracer_rl.ipynb
Click "Cell" -> "Run All"

Open reinforcement_learning/rl_deepracer_robomaker_coach_gazebo/deepracer_rl.ipynb in an Amazon SageMaker Notebook instance and run all cells to reproduce the missing training_metrics.json error. Trace the training_metrics_path and wait_for_s3_object calls, then verify that the notebook completes without the FileNotFoundError and retrieves the expected S3 object.

Written by the indexing model from the issue text.