'get rpn roidb and ground truth roidb
:param gt_roidb: ground truth roidb
:param append_gt: append ground truth
:return: roidb of rpn'

def rpn_roidb(self, gt_roidb, append_gt=False):

    if append_gt:
        logger.info(('%s    appending    ground    truth    annotations' % self.name))
        rpn_roidb = self.load_rpn_roidb(gt_roidb)
        roidb = IMDB.merge_roidbs(gt_roidb, rpn_roidb)
    else:
        roidb = self.load_rpn_roidb(gt_roidb)
    return roidb
