pulsar build and CI changes

Summary:
Changes to CI and some minor fixes now that pulsar is part of pytorch3d. Most significantly, add CUB to CI builds.

Make CUB_HOME override the CUB already in cudatoolkit (important for cuda11.0 which uses cub 1.9.9 which pulsar doesn't work well with.
Make imageio available for testing.
Lint fixes.
Fix some test verbosity.
Avoid use of atomicAdd_block on older GPUs.

Reviewed By: nikhilaravi, classner

Differential Revision: D24773716

fbshipit-source-id: 2428356bb2e62735f2bc0c15cbe4cff35b1b24b8

docs/examples/pulsar_basic.py

@@ -5,9 +5,9 @@ This example demonstrates the most trivial, direct interface of the pulsar
 sphere renderer. It renders and saves an image with 10 random spheres.
 Output: basic.png.
 """
+import logging
 import math
 from os import path
-import logging
 
 import imageio
 import torch

docs/examples/pulsar_cam_unified.py

@@ -9,8 +9,8 @@ distorted. Gradient-based optimization is used to converge towards the
 original camera parameters.
 Output: cam-pt3d.gif
 """
-from os import path
 import logging
+from os import path
 
 import cv2
 import imageio

docs/examples/pulsar_multiview.py

@@ -13,9 +13,9 @@ This example is not available yet through the 'unified' interface,
 because opacity support has not landed in PyTorch3D for general data
 structures yet.
 """
+import logging
 import math
 from os import path
-import logging
 
 import cv2
 import imageio

docs/examples/pulsar_optimization.py

@@ -8,8 +8,8 @@ The scene is initialized with random spheres. Gradient-based
 optimization is used to converge towards a faithful
 scene representation.
 """
-import math
 import logging
+import math
 
 import cv2
 import imageio

docs/examples/pulsar_optimization_unified.py

@@ -8,8 +8,8 @@ The scene is initialized with random spheres. Gradient-based
 optimization is used to converge towards a faithful
 scene representation.
 """
-import math
 import logging
+import math
 
 import cv2
 import imageio