add TestReader for ppyolo export (#1579)

configs/ppyolo/ppyolo_r18vd.yml

@@ -132,3 +132,27 @@ TrainReader:
   worker_num: 16
   bufsize: 8
   use_process: true
+
+TestReader:
+  inputs_def:
+    image_shape: [3, 320, 320]
+    fields: ['image', 'im_size', 'im_id']
+  dataset:
+    !ImageFolder
+      anno_path: annotations/instances_val2017.json
+      with_background: false
+  sample_transforms:
+    - !DecodeImage
+      to_rgb: True
+    - !ResizeImage
+      target_size: 320
+      interp: 2
+    - !NormalizeImage
+      mean: [0.485, 0.456, 0.406]
+      std: [0.229, 0.224, 0.225]
+      is_scale: True
+      is_channel_first: false
+    - !Permute
+      to_bgr: false
+      channel_first: True
+  batch_size: 1