Move upload/download image action to right place

test_update_image is used to test image update API, it's quite
confusing that the upload/download image API is called.

And there is the test for upload/download image API already:
test_register_upload_get_image_file

We should move the upload/download action to the right place.

Change-Id: I18e13cdb81c5ec3fc4abcdd8c8fb21eaf05d4675
diff --git a/tempest/api/image/v2/test_images.py b/tempest/api/image/v2/test_images.py
index c938cee..5a27a43 100644
--- a/tempest/api/image/v2/test_images.py
+++ b/tempest/api/image/v2/test_images.py
@@ -57,6 +57,13 @@
         self.assertIn('status', image)
         self.assertEqual('queued', image['status'])
 
+        # NOTE: This Glance API returns different status codes for image
+        # condition. In this empty data case, Glance should return 204,
+        # so here should check the status code.
+        image_file = self.client.show_image_file(image['id'])
+        self.assertEqual(0, len(image_file.data))
+        self.assertEqual(204, image_file.response.status)
+
         # Now try uploading an image file
         file_content = data_utils.random_bytes()
         image_file = six.BytesIO(file_content)
@@ -115,17 +122,6 @@
                                   visibility='private')
         self.assertEqual('queued', image['status'])
 
-        # NOTE: This Glance API returns different status codes for image
-        # condition. In this empty data case, Glance should return 204,
-        # so here should check the status code.
-        image_file = self.client.show_image_file(image['id'])
-        self.assertEqual(0, len(image_file.data))
-        self.assertEqual(204, image_file.response.status)
-
-        # Now try uploading an image file
-        image_file = six.BytesIO(data_utils.random_bytes())
-        self.client.store_image_file(image['id'], image_file)
-
         # Update Image
         new_image_name = data_utils.rand_name('new-image')
         self.client.update_image(image['id'], [