Set and save a cell's start state.

        Optionally called by engines during execution to initialize the
        metadata for a cell and save the notebook to the output path.

def cell_start(self, cell, cell_index=None, **kwargs):
        """
        Set and save a cell's start state.

        Optionally called by engines during execution to initialize the
        metadata for a cell and save the notebook to the output path.
        """
        if self.log_output:
            ceel_num = cell_index + 1 if cell_index is not None else ''
            logger.info('Executing Cell {:-<40}'.format(ceel_num))

        cell.metadata.papermill['start_time'] = self.now().isoformat()
        cell.metadata.papermill["status"] = self.RUNNING
        cell.metadata.papermill['exception'] = False

        self.save()