Dockerify and clean up the smoke tests

* Add a `Dockerfile`. Sadly, the `ADD` instruction needs to precede `RUN apt-get && pip install`; specifying `RUN apt-get install python-pip` followed by `ADD` and then `RUN pip install` causes pip to throw an "invalid cross-device link" exception.
* Expose `allow_dupes` and `case_sensitive_keys` as config options.
* Use random device and channel IDs generated via `os.urandom()`, since the server validates IDs now.

Depends on mozilla-services/pushgo#97.