User specific configs

This branch adds the user-specific S3 bucket and SQS queue config settings needed by hermes. It still falls back to the defaults when no user-specific config is found.

We also added some integration tests around this feature using an FTP client library (which always sends the CWD command, so I added that to the allowed list, but I'm not 100% sure that's safe).

[Pivotal card](https://www.pivotaltracker.com/story/show/71307170)

Assigned @nherzing.