Dataset autodownload feature addition (#685)

* initial commit

* move download scripts into data/scripts

* new check_dataset() function in general.py

* move check_dataset() out of with context

* Update general.py

* DDP update

* Update general.py

test.py

@@ -13,7 +13,7 @@ from tqdm import tqdm
 from models.experimental import attempt_load
 from utils.datasets import create_dataloader
 from utils.general import (
-    coco80_to_coco91_class, check_file, check_img_size, compute_loss, non_max_suppression,
+    coco80_to_coco91_class, check_dataset, check_file, check_img_size, compute_loss, non_max_suppression,
     scale_coords, xyxy2xywh, clip_coords, plot_images, xywh2xyxy, box_iou, output_to_target, ap_per_class)
 from utils.torch_utils import select_device, time_synchronized
 
@@ -68,6 +68,7 @@ def test(data,
     model.eval()
     with open(data) as f:
         data = yaml.load(f, Loader=yaml.FullLoader)  # model dict
+    check_dataset(data)  # check
     nc = 1 if single_cls else int(data['nc'])  # number of classes
     iouv = torch.linspace(0.5, 0.95, 10).to(device)  # iou vector for mAP@0.5:0.95
     niou = iouv.numel()