**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`
tests/utils/test_cli_util.py
abs_pid_path = os.path.join(os.getcwd(), "fake.pid")
        pid, _, _, _ = cli.setup_locations(process="fake_process", pid=abs_pid_path)
        assert pid == abs_pid_path
    def test_setup_locations_none_pid_path(self):
        process_name = "fake_process"
        default_pid_path = os.path.join(settings.AIRFLOW_HOME, f"airflow-{process_name}.pid")
        pid, _, _, _ = cli.setup_locations(process=process_name)
        assert pid == default_pid_path
@contextmanager
def fail_action_logger_callback():
    """
    Adding failing callback and revert it back when closed.
    :return:
    """
    tmp = cli_action_loggers.__pre_exec_callbacks[:]
    def fail_callback(**_):
        raise NotImplementedError
    cli_action_loggers.register_pre_exec_callback(fail_callback)
    yield
    cli_action_loggers.__pre_exec_callbacks = tmp
@cli.action_logging
def fail_func(_):
    raise NotImplementedError
@cli.action_logging
def success_func(_):
    pass