Misleading exception when lock_path is not provided

When lock_file is not present on the [oslo_concurrency] section of the config file, we are getting a misleading error saying that it is not preset on the DEFAULT group:

Captured traceback:
~~~~~~~~~~~~~~~~~~~
    Traceback (most recent call last):

      File "/home/tbrito/workspace/openstack/nova/nova/tests/unit/virt/test_block_device.py", line 725, in test_volume_attach_with_shared_targets
    self.test_volume_attach(include_shared_targets=True)

      File "/home/tbrito/workspace/openstack/nova/nova/tests/unit/virt/test_block_device.py", line 721, in test_volume_attach
    self._test_volume_attach(test_bdm, self.volume_bdm, volume,

      File "/home/tbrito/workspace/openstack/nova/.tox/py39/lib/python3.9/site-packages/mock/mock.py", line 1346, in patched
    return func(*newargs, **newkeywargs)

      File "/home/tbrito/workspace/openstack/nova/nova/tests/unit/virt/test_block_device.py", line 623, in _test_volume_attach
    driver_bdm.attach(self.context, instance,

      File "/home/tbrito/workspace/openstack/nova/nova/virt/block_device.py", line 46, in wrapped
    ret_val = method(obj, context, *args, **kwargs)

      File "/home/tbrito/workspace/openstack/nova/nova/virt/block_device.py", line 668, in attach
    with brick_utils.guard_connection(volume):

      File "/usr/lib/python3.9/contextlib.py", line 119, in __enter__
    return next(self.gen)

      File "/home/tbrito/workspace/openstack/nova/.tox/py39/lib/python3.9/site-packages/os_brick/initiator/utils.py", line 45, in guard_connection
    with lockutils.lock(device['service_uuid'], 'os-brick-',

      File "/usr/lib/python3.9/contextlib.py", line 119, in __enter__
    return next(self.gen)

      File "/home/tbrito/workspace/openstack/nova/.tox/py39/lib/python3.9/site-packages/oslo_concurrency/lockutils.py", line 297, in lock
    ext_lock = external_lock(name, lock_file_prefix, lock_path)

      File "/home/tbrito/workspace/openstack/nova/.tox/py39/lib/python3.9/site-packages/oslo_concurrency/lockutils.py", line 189, in external_lock
    lock_file_path = _get_lock_path(name, lock_file_prefix, lock_path)

      File "/home/tbrito/workspace/openstack/nova/.tox/py39/lib/python3.9/site-packages/oslo_concurrency/lockutils.py", line 183, in _get_lock_path
    raise cfg.RequiredOptError('lock_path')

    oslo_config.cfg.RequiredOptError: value required for option lock_path in group [DEFAULT]

https://github.com/openstack/oslo.concurrency/blob/master/oslo_concurrency/lockutils.py#L180