Add failure reason for execution timeout

What does this MR do?

Today, we handle execution timeout failure as script failure, which does not show any messages at the top of job log page.

We should show the failure as execution timeout, which indicates that the job reached the limit that users can set in project/runner setting pages.

• GitLab-rails CE: Here
• GitLab-rails EE: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/7860
• GitLab-runner: gitlab-runner!1051 (merged)

The copy is The script exceeded the maximum execution time set for the job.

What are the relevant issue numbers?

There are no issues

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [-] Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides