Support for cleaning downloaded models and preprocessed datasets for Nvidia implementation

[arjunsuresh]

In Nvidia implementation we either download or copy the models and datasets to the concerned path in the NVIDIA_SCRATCH_PATH. It'll be good to have a CM script to clean them as otherwise users will need to find this path if they want to clean some of the data. The CM script should support all the models as variations and also the below three variations for the artifact to be cleaned.

• models
• preprocessed_data
• downloaded_data