Fixed issue when container does not have a environment variables.

nginx_proxy.py

@@ -47,6 +47,8 @@ def analyse_env_vars(inspect_data):
     """Extracts the environment variables from the given result of an 'inspect
         container' call."""
     env_data = {}
+    if not 'Env' in inspect_data['Config'] or inspect_data['Config']['Env'] is None:
+        return env_data
     for env_var in inspect_data['Config']['Env']:
         t = env_var.split("=")
         env_data[t[0]] = t[1]