Manila returns Python error when passing optional arguments without using a subcommand

[Eduardo Santos]

Steps to reproduce
==================
* I ran the `manila` command without a subcommand while
passing at least one optional argument

Some of the commands in which the bug occurs:
- manila --os-cache
- manila --os-reset-cache
- manila --os-user-id 123
- manila --os-project-name foo

The `--version` argument is an exception.

Expected result
===============
It should display the help message.

Actual result
=============
ERROR: 'Namespace' object has no attribute 'func'

Environment
===========
1. Branch master

Logs & Configs
==============
http://paste.openstack.org/show/799687/

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/761654
Committed: https://git.openstack.org/cgit/openstack/python-manilaclient/commit/?id=aeb47213eaa8f27bea43bb6b915d6be255a9e246
Submitter: Zuul
Branch: master

commit aeb47213eaa8f27bea43bb6b915d6be255a9e246
Author: Eduardo Santos <email address hidden>
Date: Thu Nov 5 18:27:55 2020 +0000

    Fix undesirable raw Python error

    Using the manilaclient without a subcommand while
    passing an optional argument triggers the raw Python
    error `ERROR: 'Namespace' object has no attribute
    'func'`. This bug can be reproduced by issuing the
    command `manila --os-cache`.
    Added a default value to `func` and an empty value to
    `command` as placeholders so that a help message is
    shown instead of the Python error.
    This patch uses the same fix implemented in the
    python-cinderclient.

    Closes-Bug: #1902873
    Change-Id: I5fcafd4bdfb40b2054e1205c14493c2f4be1f77a

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/python-manilaclient 2.4.0 release.