find_resultrow: handle rows that differ only by env
    
    I sure do like making life hard for myself. By adding the i386
    variant tables to Installation, I made it so there are result
    rows with the same testcase, testname and section; they differ
    only in the environments they store results for. So we make
    `find_resultrow` work for this case and use it in
    `report_validation_results`.