'turn rpn detection boxes into roidb
:param gt_roidb: [image_index][\'boxes\', \'gt_classes\', \'gt_overlaps\', \'flipped\']
:return: roidb: [image_index][\'boxes\', \'gt_classes\', \'gt_overlaps\', \'flipped\']'

def load_rpn_roidb(self, gt_roidb):

    box_list = self.load_rpn_data()
    return self.create_roidb_from_box_list(box_list, gt_roidb)
