We can't use dummy app for tests

```
TypeError: Cannot read property 'outputPath' of undefined
at app.use (/Users/davidlaird/projects/ember-cli-fastboot/index.js:313:42)
```
The `ember-cli-fastboot` addon needs to come before `broccoli-serve-files` to SSR files.

Running the dummy app will result in the following error

```
TypeError: Cannot read property 'outputPath' of undefined
at app.use (/Users/davidlaird/projects/ember-cli-fastboot/index.js:313:42)
```

https://github.com/ember-fastboot/ember-cli-fastboot/blob/master/index.js#L325

The list of addons (truncated) when running the dummy app.
```
[ 'testem-url-rewriter',
'ember-cli-fastboot',
'tests-server-middleware',
'history-support-middleware',
'live-reload-middleware',
'broccoli-watcher',
'broccoli-serve-files',
'proxy-server-middleware',
...
'ember-cli-babel' ]
```

This an app list of addons (truncated) with Fastboot SSR it's files.
```
[ 'amd-transform',
'tests-server-middleware',
'history-support-middleware',
'live-reload-middleware',
'broccoli-watcher',
'ember-cli-fastboot',
'broccoli-serve-files',
'proxy-server-middleware',
...
'ember-source',
'ember-welcome-page',
'qunit-dom' ]
```