add mosaic and warmup to hyperparameters (#931)

utils/datasets.py

@@ -516,7 +516,8 @@ class LoadImagesAndLabels(Dataset):  # for training/testing
             index = self.indices[index]
 
         hyp = self.hyp
-        if self.mosaic:
+        mosaic = self.mosaic and random.random() < hyp['mosaic']
+        if mosaic:
             # Load mosaic
             img, labels = load_mosaic(self, index)
             shapes = None
@@ -550,7 +551,7 @@ class LoadImagesAndLabels(Dataset):  # for training/testing
 
         if self.augment:
             # Augment imagespace
-            if not self.mosaic:
+            if not mosaic:
                 img, labels = random_perspective(img, labels,
                                                  degrees=hyp['degrees'],
                                                  translate=hyp['translate'],