allow missing carla environment and missing matplotlib package

agents/policy_gradients_agent.py

@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2017 Intel Corporation 
+# Copyright (c) 2017 Intel Corporation
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -18,7 +18,11 @@ from agents.policy_optimization_agent import *
 import numpy as np
 from logger import *
 import tensorflow as tf
-import matplotlib.pyplot as plt
+try:
+    import matplotlib.pyplot as plt
+except:
+    from logger import failed_imports
+    failed_imports.append("matplotlib")
 
 from utils import *