Allow to dedicate a journal by OSD.

Please note that now you have to specify the full path of the device, ie /dev/something (for OSD and for journal).
This is the proof you break backward compatibility, you have to modify parameters in the unit test, which reflects the configuration a deployer could have.
In your case, you should not touch the existing unit tests to validate they still work. That would validate backward compatibility.
Also, you should add a new unit test to validate the feature you're adding, with a "context", like we do in others unit tests.