Exit properly from EADDRINUSE.

Closes #1314.

```
_____ember-cli-test master % ember server
version: 0.0.39-exit-properly-c791a21573

Livereload failed on port 35729.  It is either in use or you do not have permission.
```
i think we should use branding instead of instanceof checks, as plugins that throw this error wont pass the instanceof check