Test gltf texture without renderer.

Summary:
Change the cow gltf loading test to validate the texture values and not to validate the renderer output because it has an unstable pixel.

Also a couple of lints.

Reviewed By: patricklabatut

Differential Revision: D29131260

fbshipit-source-id: 5e11f066a2a638588aacb09776cc842173ef669f

tests/test_shader.py

@@ -4,10 +4,7 @@ import unittest
 
 import torch
 from common_testing import TestCaseMixin
-from pytorch3d.renderer.cameras import (
-    look_at_view_transform,
-    PerspectiveCameras,
-)
+from pytorch3d.renderer.cameras import PerspectiveCameras, look_at_view_transform
 from pytorch3d.renderer.mesh.rasterizer import Fragments
 from pytorch3d.renderer.mesh.shader import (
     HardFlatShader,