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.
Merge pull request #1336 from deis/1326-container-config

fix(controller/registry): add old config vars
Merge branch 'master' of https://github.com/deis/deis