don't reap jobs that aren't running

this is a simple sanity check, but it should help us avoid shooting
ourselves in the foot in complicated scenarios, such as:

1.  A dispatcher worker is running a job, and it's killed with `kill -9`
2.  The dispatcher attempts to reap jobs with a matching celery_task_id
3.  The associated sync project update has the *same* celery_task_id
    (an implementation detail of how we implemented that), and it ends
    up getting reaped _even though_ it's already finished and has
    status=successful

awx/main/dispatch/reaper.py

@@ -11,6 +11,9 @@ logger = logging.getLogger('awx.main.dispatch')
 
 
 def reap_job(j, status):
+    if UnifiedJob.objects.get(id=j.id).status not in ('running', 'waiting'):
+        # just in case, don't reap jobs that aren't running
+        return
     j.status = status
     j.start_args = ''  # blank field to remove encrypted passwords
     j.job_explanation += ' '.join((