Clear the current candidates.

        :param bool clear_env:
            If ``True``, clears also environment's (or its underlying slave
            environments') candidates.

def clear_candidates(self, clear_env=True):
        """Clear the current candidates.

        :param bool clear_env:
            If ``True``, clears also environment's (or its underlying slave
            environments') candidates.
        """
        async def slave_task(addr):
            r_manager = await self.env.connect(addr)
            return await r_manager.clear_candidates()

        self._candidates = []
        if clear_env:
            if self._single_env:
                self.env.clear_candidates()
            else:
                mgrs = self.get_managers()
                run(create_tasks(slave_task, mgrs))