Bug 1078128 - [Settings] remove try_show_homescreen_section.js and move this logic into root.js

...to root.js
It would be more readable to do things like:
```
appsCache._initApps().then(function() {
  assert.equal(appsCache._apps, testApps);
}, function() {
  // 
}).then(done, done);
MockMozApps.mTriggerGetAllAppsCallback();
```