support train model for infer MODE

tests/ocr_det_params.txt

@@ -34,8 +34,8 @@ distill_export:null
 export1:null
 export2:null
 ##
-infer_model:./inference/ch_ppocr_mobile_v2.0_det_infer/
-infer_export:null
+infer_model:./inference/ch_ppocr_mobile_v2.0_det_train/best_accuracy
+infer_export:tools/export_model.py -c configs/det/det_mv3_db.yml -o
 infer_quant:False
 inference:tools/infer/predict_det.py
 --use_gpu:True|False