Add JSON schema for job API
Problem to solve
In gitlab-ce!21328 spec/fixtures/api/schemas/job/job_details.json was introduced but has missing properties as discussed in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/21328#note_95877753
Update the JSON schema to reflect every property that jobs/:id.josn return
Links / references
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/21328#note_98515279
gitlab-ce!21328