Detect alternate location of secret file when it is moved into the /config/rubber dir on remote servers.

If you named your sercet file as /secret/rubber-secret.yml, this would work by accident since it would be picked up by the `read_config method`, not the `read_secret_config method`
Merge pull request #456 from johnnyshields/fix-obfus-secret

Bugfix for obfuscated secret file location on remote servers