T138 - /testcases/{testcase_name}/results and /jobs/{job_id}/results should return 404
    
    Summary: The API now checks whether the testcase/job exists, and throws 404 if it does not, instead of silently returning empty results set.
    
    Test Plan: NaN
    
    Reviewers: mkrizek, tflink
    
    CC: tflink
    
    Differential Revision: https://phab.qadevel.cloud.fedoraproject.org/D75