job_monitor: removes unnecessary calls to k8s api
job_monitor: removes unnecessary calls to k8s api

* Closes #227

tiborsimko/reana-job-controller,diegodelemos/reana-job-controller,reanahub/reana-job-controller,diegodelemos/reana-job-controller,reanahub/reana-job-controller,tiborsimko/reana-job-controller