Bug 918970 - display existing thread when sending a sms from contact app

old PR : https://github.com/mozilla-b2g/gaia/pull/16216

I copy my comment on the commit. Don't know why it didn't happen here as well :

So for this test, I relied on stubbing focus (which is mocked anyway) because Navigation.toPanel is called before Compose.focus. So spying toPanel was not enough to wait for focus to be called.

The main drawback of this solution is that is case Compose.focus is not called, the test fails because of the timeout, which is not ideal. Do you have a better idea? I didn't see anything to spy on to make things better.