glance-manage: fix crash under Python3.11
glance-manage: fix crash under Python3.11

In Python3.11, the argparse module became stricter. While the following
code was fine in previous versions, it will now raise an
argparse.ArgumentError because we added the same subparser twice:

import argparse
parser = argparse.ArgumentParser()
subparsers = parser.add_subparsers(title='Commands')
subparsers.add_parser('foo')
subparsers.add_parser('foo')
subparsers.add_parser('bar')
parser.parse_args()

This mistake was silently ignore in Python3.10, which explains why this
was never an issue for glance-manage.

Closes-Bug: #1982426
Change-Id: I3a88ab5d2e67a1553f03b0b8ba44efbef976ffb0

openstack/glance,openstack/glance,openstack/glance