Bug 1112334 - Write a test for basic Find My Device logging in existing ...

...account
It could be that that is needed. My plan is indeed to also create a "not signed in" testcase, but then I need to delete the account afterwards on the website, which is a little bit more involved, so that's why I waited on that.
At this point, I don't know if I need to have this distinction at all between FindMyDeviceSignedIn and FindMyDeviceNotSignedIn, so I'd rather wait on that, before I get to that, if you don't mind. So I would prefer to just use FindMyDevice and I'll refactor it when it is needed for the new test, ok?