[Enhance] Replace data_dict calling 'img' key to support MMDet3D (#514)

* remove dict calling img key for compatibility

* fix unit test

* infer batch size using len(result) to be consistent with mmcv

mmseg/apis/test.py

@@ -97,7 +97,7 @@ def single_gpu_test(model,
                 result = np2tmp(result)
             results.append(result)
 
-        batch_size = data['img'][0].size(0)
+        batch_size = len(result)
         for _ in range(batch_size):
             prog_bar.update()
     return results

mmseg/models/segmentors/base.py

@@ -155,7 +155,7 @@ class BaseSegmentor(nn.Module):
         outputs = dict(
             loss=loss,
             log_vars=log_vars,
-            num_samples=len(data_batch['img'].data))
+            num_samples=len(data_batch['img_metas']))
 
         return outputs