updatehub: runtime_settings: move tests under a module
updatehub: runtime_settings: move tests under a module

We will be adding more tests so to make it easier to follow we are
adding the existing tests under a `tests` module.

Signed-off-by: Otavio Salvador <1d31b11c1b92bf5d043d36edfe7174db39a6b891@ossystems.com.br>

UpdateHub/updatehub