tests: introduce qemucapsfixreplies helper
    
    Sometimes we don't regenerate QEMU capabilities replies using QEMU
    binary but we simply add a new entry manually.  In that case you need
    to manually fix all the replies ids.  This helper will do that for you.
    
    Reviewed-by: Andrea Bolognani <abologna@redhat.com>
    Signed-off-by: Pavel Hrdina <phrdina@redhat.com>