infra: fix list_images.py for build images (google#14152)

Signed-off-by: David Korczynski <david@adalogics.com>

Author: DavidKorczynski

infra/base-images/list_images.py

@@ -29,8 +29,8 @@
 
 import base_images
 
-for image_config in base_images.BASE_IMAGES:
+for image_config in base_images.BASE_IMAGE_DEFS:
   # Exclude 'base-clang-full' as it is a special case not intended for
   # the general build script.
-  if image_config.name != 'base-clang-full':
-    print(image_config.name)
+  if image_config.get('name', '') != 'base-clang-full':
+    print(image_config.get('name', ''))