- simplify the configuration module
the `package` attribute makes little sense to be user-configurable,
since it will always need to be the derivation defined in this very
repository. for debugging one may as well change the original code itself.
- unbreak deployment
setting `CREDENTIALS_DIRECTORY` disabled the systemd mechanism set up
in the configuration module.
- remove unneeded configuration for deployment
- unbreak integration tests
before that missed waiting for the service to create some
state before running the application-level tests.