Schema for data in CollectorStage.

def schema_complete():
        """Schema for data in CollectorStage."""
        return Schema({
            'stage': And(str, len),
            'status': And(str, lambda s: s in ['started', 'succeeded', 'failed']),
            Optional('events', default=[]): And(len, [CollectorStage.schema_event_items()])
        })