Add tests for NMonad.DBus that spawn temp daemons in containers

To have tests that cover the `NMonad.DBus` module, it is necessary to make use of DBus daemons, preferably running inside temporary test containers.

Running containers for unit / integration tests is not a new concept, and support for them exists in Haskell to a limited extended in [testcontainers](https://hackage.haskell.org/package/testcontainers-0.5.0.0). In fact, work into this has been done in [test/add-dbus-tests](https://github.com/d3adb5/nmonad/tree/test/add-dbus-tests).

DBus authentication and the very package for Haskell have proven to be a bit of a roadblock. Running commands inside provisioned containers, which is straightforward when working with test containers in imperative languages, is also something to look into so we do not depend on packages being installed locally.