text: Title: API docs for job status should clearly explain what fields indicate success or failure
  Body: The API docs for jobs are unclear as to what fields a caller would use to determine job success or failure in 1.11 (and we haven't updated them in a while)
  
  ```
    status:
      conditions:
      - lastProbeTime: 2018-09-15T19:51:27Z
        lastTransitionTime: 2018-09-15T19:51:27Z
        message: Job has reached the specified backoff limit
        reason: BackoffLimitExceeded
        status: "True"
        type: Failed
      failed: 6
      startTime: 2018-09-15T19:46:13Z
  ```
  
  ```
  $ kubectl explain jobs.status
  KIND:     Job
  VERSION:  batch/v1
  
  RESOURCE: status <Object>
  
  DESCRIPTION:
       Current status of a job. More info:
       https://git.k8s.io/community/contributors/devel/api-conventions.md#spec-and-status
  
       JobStatus represents the current state of a Job.
  
  FIELDS:
     active	<integer>
       The number of actively running pods.
  
     completionTime	<string>
       Represents time when the job was completed. It is not guaranteed to be set
       in happens-before order across separate operations. It is represented in
       RFC3339 form and is in UTC.
  
     conditions	<[]Object>
       The latest available observations of an object's current state. More info:
       https://kubernetes.io/docs/concepts/workloads/controllers/jobs-run-to-completion/
  
     failed	<integer>
       The number of pods which reached phase Failed.
  
     startTime	<string>
       Represents time when the job was acknowledged by the job controller. It is
       not guaranteed to be set in happens-before order across separate
       operations. It is represented in RFC3339 form and is in UTC.
  
     succeeded	<integer>
       The number of pods which reached phase Succeeded.
  ```
  
  A casual reader would infer that completionTime is set when the job fails (but it isn't).  Linking out to the docs is ok, but I shouldn't have to click through the links to understand how to use the Job object.  The Job description and the job status fields should *clearly* indicate what fields are set in completion states on the job, because that's 100% of the point of docs.  Taking a summary of the jobs-run-to-completion link and putting it in job.status.conditions, job.status, and job would improve the actual utility of our API doc.
  
  We should also do a pass on other objects and make the actual in server docs more useful.
  
  @kubernetes/sig-apps-bugs 