os-api-ref: yaml error in parameters.yaml does not report properly

[Chris Dent]

Using os-api-ref: 1.6.1

If there is an error in the YAML in parameters.yaml the error handling to report that error doesn't work, instead:

Exception occurred:
  File "/Users/cdent/src/placement/.tox/docs/lib/python3.7/site-packages/os_api_ref/__init__.py", line 236, in _load_param_file
    LOG.exception(exc_info=exc)
TypeError: exception() missing 1 required positional argument: 'msg'

which corresponds with: https://opendev.org/openstack/os-api-ref/src/commit/f8557cb63dc2c8a9b8f56b25318e9b600da00c75/os_api_ref/__init__.py#L232

The real error in this case was:

while parsing a block mapping
  in "/Users/cdent/src/placement/api-ref/source/parameters.yaml", line 2, column 1
expected <block end>, but found '<block mapping start>'
  in "/Users/cdent/src/placement/api-ref/source/parameters.yaml", line 477, column 3

which I was able to fix once I knew what it was.