Retrieve the API params from the config file.

def _get_api_params(api_url=None,
                    api_version=None,
                    api_key=None):
    '''
    Retrieve the API params from the config file.
    '''
    mandrill_cfg = __salt__['config.merge']('mandrill')
    if not mandrill_cfg:
        mandrill_cfg = {}
    return {
        'api_url': api_url or mandrill_cfg.get('api_url') or BASE_URL,  # optional
        'api_key': api_key or mandrill_cfg.get('key'),  # mandatory
        'api_version': api_version or mandrill_cfg.get('api_version') or DEFAULT_VERSION
    }