Split feature tests out to different build job

**What does this MR do?**
This MR is a follow up to: https://github.com/gitlabhq/gitlabhq/pull/6753 since it turns out that only splitting API tests out was not sufficient. At this point I've taken a look at how long the `spec/features` tests took to run on bare metal: `15 minutes`. So i think that would be a great candidate to be in a separate build job.

Also I did a line count for every type of spec we have, so maybe its a good idea to also split out the model specs. But lets see if this has any effect first:
```
Controllers: 340
Requests: 3226
Mailers: 560
Finders: 142
Services: 1440
Observers: 178
Lib: 841
Models: 3335
Features: 2232
```