Creates or updates the symlink to group_vars and returns None.

        :returns: None

def _link_or_update_vars(self):
        """
        Creates or updates the symlink to group_vars and returns None.

        :returns: None
        """
        for d, source in self.links.items():
            target = os.path.join(self.inventory_directory, d)
            source = os.path.join(self._config.scenario.directory, source)

            if not os.path.exists(source):
                msg = "The source path '{}' does not exist.".format(source)
                util.sysexit_with_message(msg)
            msg = "Inventory {} linked to {}".format(source, target)
            LOG.info(msg)
            os.symlink(source, target)