fix(controller/registry): add old config vars

In child images, we weren't dumping the old config variables from
previous images. This would fester and would run into issues such as
environment variables going missing. Adding them back solves this issue.

Author: Matthew Fisher

registry/private.py

@@ -151,7 +151,7 @@ def _construct_env(env, config):
         if k in config:
             # update values defined by config
             v = config.pop(k)
-            new_env.append("{}={}".format(k, v))
+        new_env.append("{}={}".format(k, v))
     # add other config ENV items
     for k, v in config.items():
         new_env.append("{}={}".format(k, v))