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