**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
"""
    Returns without error on SIGINT or SIGTERM signals in interactive command mode
    e.g. CTRL+C or kill <PID>
    """
    sys.exit(0)
def sigquit_handler(sig, frame):  
    """
    Helps debug deadlocks by printing stacktraces when this gets a SIGQUIT
    e.g. kill -s QUIT <PID> or CTRL+\
    """
    print(f"Dumping stack traces for all threads in PID {os.getpid()}")
    id_to_name = {th.ident: th.name for th in threading.enumerate()}
    code = []
    for thread_id, stack in sys._current_frames().items():  
        code.append(f"\n# Thread: {id_to_name.get(thread_id, '')}({thread_id})")
        for filename, line_number, name, line in traceback.extract_stack(stack):
            code.append(f'File: "{filename}", line {line_number}, in {name}')
            if line:
                code.append(f"  {line.strip()}")
    print("\n".join(code))
class ColorMode:
    """Coloring modes. If `auto` is then automatically detected."""
    ON = "on"
    OFF = "off"
    AUTO = "auto"
def should_use_colors(args) -> bool: