fix testing a different arch than system arch
    
    Arch needs to be dynamically determined from the packages to be tested
    (which we didn't use to do), otherwise dependency checking fails with
    error 'package NVR does not have a compatible architecture'.
    
    Even though it's completely pretty, use `dependency_analyzer_from_args()`
    method from rpmdeplint that takes care of everything for us, we just
    need to fake the args.