Add tests for CI statuses rendered in UI

Description

In https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7889 we were refining CI statuses to encapsulate core statuses in separate classes. I was integrating new statuses into existing ci_status_helpers which caused some problems in my local development environment.

The problem is that commit that introduced this incorrect behavior passed in our CI, which means that we have insufficient amount of feature tests for CI statuses being rendered in merge request widget.

Proposal

Add feature tests for CI status being rendered in merge request widget.

/cc @ayufan