connect method does not raise on missing auth params

[Yanks]

in openstack/__init__.py def connect, the docstring mentions
```
:raises: keystoneauth1.exceptions.MissingRequiredOptions on missing required auth parameters
```

However, when providing an invalid clouds.yaml (commented out auth params, deleted auth params), i.e.
```
clouds:
  sunbeam:
    auth:
      auth_url: http://10.20.21.12/openstack-keystone
# password: 8gfWnW157KJ7
# project_domain_name: admin_domain
# project_name: admin
# user_domain_name: admin_domain
# username: admin
```
this does not raise keystoneauth1.exceptions.MissingRequiredOptions.