don't write anything to stdout or stderr
    
    Removed some superfluous print statements which were presumably added
    for debugging.
    
    Capture the stderr of rpmbuild and createrepo_c, so that we don't see it
    normally. If the command fails, the exception message will include the
    output from the command, which makes it easier to figure out what went
    wrong if they do fail.
    
    The end result is that rpmfluff itself, as well as its test suite, can
    run without producing any spew.