Bug 1057850 - Play busy tone when the remote party terminates the call setup with busy as reason

See bug https://bugzilla.mozilla.org/show_bug.cgi?id=1057850 please.
Instead of this, we need to control when the tone is over. We should add a listener to 'ended' event in the TonePlayer (https://developer.mozilla.org/en-US/docs/Web/Guide/Events/Media_events) and use something like:
`TonePlayerHelper.stop(callback)` or use a promise if you are more confortable with (`TonePlayerHelper.stop().then(....)`)