**Apache Airflow version**:
2.0.1

**Kubernetes version (if you are using kubernetes)** (use `kubectl version`):

**Environment**:

- **Cloud provider or hardware configuration**: 4GB RAM, Processor - Intel(R) Core(TM) i5-8250U CPU @ 1.60GHz
- **OS** (e.g. from /etc/os-release): 18.04.5 LTS (Bionic Beaver)
- **Kernel** (e.g. `uname -a`): Linux 4.15.0-136-generic
- **Install tools**: bare metal installation as per commands given [here](https://airflow.apache.org/docs/apache-airflow/stable/installation.html)

**What happened**:

On running `airflow scheduler -p` got following error:-
```
Traceback (most recent call last):
  File "/home/vineet/Documents/projects/venv/bin/airflow", line 8, in <module>
    sys.exit(main())
  File "/home/vineet/Documents/projects/venv/lib/python3.6/site-packages/airflow/__main__.py", line 40, in main
    args.func(args)
  File "/home/vineet/Documents/projects/venv/lib/python3.6/site-packages/airflow/cli/cli_parser.py", line 48, in command
    return func(*args, **kwargs)
  File "/home/vineet/Documents/projects/venv/lib/python3.6/site-packages/airflow/utils/cli.py", line 86, in wrapper
    metrics = _build_metrics(f.__name__, args[0])
  File "/home/vineet/Documents/projects/venv/lib/python3.6/site-packages/airflow/utils/cli.py", line 118, in _build_metrics
    full_command[idx + 1] = "*" * 8
IndexError: list assignment index out of range
```
As per docs, `-p` flag is a valid flag and gives correct result for `airflow scheduler --do-pickle`

**How to reproduce it**:
Install `airflow` 2.0.1 and run `airflow scheduler -p`
airflow/utils/cli.py
if command.startswith(f'{sensitive_field}='):
                    full_command[idx] = f'{sensitive_field}={"*" * 8}'
    metrics = {
        'sub_command': func_name,
        'start_datetime': datetime.utcnow(),
        'full_command': f'{full_command}',
        'user': getpass.getuser(),
    }
    if not isinstance(namespace, Namespace):
        raise ValueError(
            "namespace argument should be argparse.Namespace instance," f"but is {type(namespace)}"
        )
    tmp_dic = vars(namespace)
    metrics['dag_id'] = tmp_dic.get('dag_id')
    metrics['task_id'] = tmp_dic.get('task_id')
    metrics['execution_date'] = tmp_dic.get('execution_date')
    metrics['host_name'] = socket.gethostname()
    extra = json.dumps({k: metrics[k] for k in ('host_name', 'full_command')})
    log = Log(
        event=f'cli_{func_name}',
        task_instance=None,
        owner=metrics['user'],
        extra=extra,
        task_id=metrics.get('task_id'),
        dag_id=metrics.get('dag_id'),
        execution_date=metrics.get('execution_date'),
    )
    metrics['log'] = log
    return metrics
def process_subdir(subdir: Optional[str]):