Fix /stasis/res/app_replaced unit test.

A typo in recent changes caused the JSON ApplicationReplaced message to
fail to build, so the message wasn't being sent out the WebSocket.

Related, the replaced application would also unregister itself when it
disconnected, which would actually unregister the new application. This
was also fixed.


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@395527 f38db490-d61c-443f-a65b-d21fe96a405b