Refactor try_delete_jobs()
Refactor try_delete_jobs()

Also tweak its error message

dreamhost/teuthology,tchaikov/teuthology,t-miyamae/teuthology,dmick/teuthology,dmick/teuthology,robbat2/teuthology,ktdreyer/teuthology,ceph/teuthology,robbat2/teuthology,ivotron/teuthology,zhouyuan/teuthology,ivotron/teuthology,michaelsevilla/teuthology,ceph/teuthology,ktdreyer/teuthology,tchaikov/teuthology,caibo2014/teuthology,SUSE/teuthology,dmick/teuthology,SUSE/teuthology,dreamhost/teuthology,yghannam/teuthology,t-miyamae/teuthology,caibo2014/teuthology,yghannam/teuthology,zhouyuan/teuthology,SUSE/teuthology,michaelsevilla/teuthology