Clear custom-targets uppon setting new taregts.json location

Author: theotherjimmy

tools/targets/__init__.py

@@ -169,6 +169,7 @@ def set_targets_json_location(location=None):
         """Set the location of the targets.json file"""
         Target.__targets_json_location = (location or
                                           Target.__targets_json_location_default)
+        Target.__extra_target_json_files = []
         # Invalidate caches, since the location of the JSON file changed
         CACHES.clear()