Add a 1s delay between each down key in do_bootloader
    
    and call save_screenshot to visually check
    for debug purpose only
    Also change for PowerPC the number of down key to 12
    (rather than 12)
    Seems to be mandatory since 20170327.
    
    Signed-off-by: Michel Normand <normand@linux.vnet.ibm.com>