'Get the config option for a domain.
:param domain_id: the domain for this option
:param group: the group name
:param option: the option name
:param sensitive: whether the option is sensitive
:returns: dict containing group, option and value
:raises keystone.exception.DomainConfigNotFound: the option doesn\'t
exist.'

@abc.abstractmethod
def get_config_option(self, domain_id, group, option, sensitive=False):

    raise exception.NotImplemented()
