Allow more configurability in production builds.

```
DISABLE_ES3=true DISABLE_JSHINT=true DISABLE_MIN=true ember serve --environment=production
```

Takes initial production build time from 70s to 21s, and rebuilds from
6s to 2s.
Merge pull request #9391 from rwjblue/more-configurability-for-prod-builds

Allow more configurability in production builds.