Sanity check plugin options values.

def check_arguments(cls, conf):
        """
        Sanity check plugin options values.

        """
        # Checking the specified list of basic health monitor plugins, which
        # should be run by the multi plugin.
        if not conf.get('multi_plugins'):
            raise ArgsError("A specification of health monitor plugins "
                            "is required (--multi_plugins).")

        # Now check parameters for all sub-plugins. We use the list of classes
        # for sub-plugins that we discovered earlier while adding parameters
        # for those sub-plugins.
        for mpc in cls.multi_plugin_classes:
            mpc.check_arguments(conf)