nemo2riva Can't instantiate abstract class ModelPT with abstract methods
**Describe the bug**

I'm trying to convert a CitriNet model I trained with NeMo v1.7.0 to the Riva format using the `nemo2riva` CLI tool.
Everytime I run:

```sh
nemo2riva --out my-model.riva my-model.nemo
```
I get the following error:

```sh
ERROR: Failed to restore model from NeMo file : my-model.nemo. Please make sure you have the latest NeMo package installed with [all] dependencies.
Traceback (most recent call last):
  File "/home/allabana/.virtualenvs/nm-debug/bin/nemo2riva", line 8, in <module>
    sys.exit(nemo2riva())
  File "/home/allabana/.virtualenvs/nm-debug/lib/python3.8/site-packages/nemo2riva/cli/nemo2riva.py", line 50, in nemo2riva
    Nemo2Riva(args)
  File "/home/allabana/.virtualenvs/nm-debug/lib/python3.8/site-packages/nemo2riva/convert.py", line 42, in Nemo2Riva
    raise e
  File "/home/allabana/.virtualenvs/nm-debug/lib/python3.8/site-packages/nemo2riva/convert.py", line 35, in Nemo2Riva
    model = ModelPT.restore_from(restore_path=nemo_in)
  File "/home/allabana/.virtualenvs/nm-debug/lib/python3.8/site-packages/nemo/core/classes/modelPT.py", line 270, in restore_from
    instance = cls._save_restore_connector.restore_from(
  File "/home/allabana/.virtualenvs/nm-debug/lib/python3.8/site-packages/nemo/core/connectors/save_restore_connector.py", line 136, in restore_from
    instance = calling_cls.from_config_dict(config=conf)
  File "/home/allabana/.virtualenvs/nm-debug/lib/python3.8/site-packages/nemo/core/classes/common.py", line 473, in from_config_dict
    instance = cls(cfg=config)
TypeError: Can't instantiate abstract class ModelPT with abstract methods list_available_models, setup_training_data, setup_validation_data
```

I've tried every combination of `nemo2riva` and `nemo_toolkit` from 1.7.0-1.10.0 and 1.3.0-1.7.0 respectively.
I would install using:

```sh
# X = [7, 8, 9, 10]
pip install  nemo2riva-1.X.0b0-py3-none-any.whl
# X = [3, 4, 5, 6, 7]
pip install 'nemo_toolkit[all]==1.X.0'
```

**Steps/Code to reproduce bug**

Use any nemo model, including the pretrained citrinet models and try to convert it

```sh
ngc registry resource download-version "nvidia/riva/riva_quickstart:1.10.0-beta"
cd riva_quickstart_v1.10.0-beta
pip install nemo2riva-1.10.0b0-py3-none-any.whl
nemo2riva --out my-model.riva my-model.nemo
```

**Expected behavior**

`nemo2riva` converts the model succesfully.

**Environment overview (please complete the following information)**

 - Environment location: Docker and Bare metal
 - Method of NeMo install: `pip install 'nemo_toolkit[all]==1.7.0'`
 - If method of install is [Docker], provide `docker pull` & `docker run` commands used
 Using Docker image `nvcr.io/nvidia/riva/riva-speech:1.10.0-beta-servicemaker`

**Environment details**

Docker and local
Otherwise, please provide:
- OS version: Ubuntu 20.04
- PyTorch version: 1.10.0
- Python version: 3.8

**Additional context**

GPU model: RTX 3090
