Modified convert_to_tarred_audio_dataset.py to accept another argument also as input
This pull request **introduces 2 alerts** when merging 1ce64a75065b53909e042395c27bf1a35f68309d into b4040fb37350ae86b64a5f53be911371d7a3879d - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-8c2c9c4c374e615c273837a54858c8611874091b)

**new alerts:**

* 1 for Unused local variable
* 1 for Unused import Could you sign the commits (instructions are provided in the dco bot output), and explain your reasoning for dataset paths argument?

Tarred datasets flatten all paths, and you can create them from a provided dataset directory and write then to another directory, so this flag is odd.  Created merge request for wrong branch
The newly added argument(dataset_dir) is concatenated with the path obtained from the manifest file. This solves the problem of FileNotFoundError as an absolute path is given for the datasets.