Add support to chain a hdd boot in the pxelinux parser

[Geoff Levand]

On 9/24/20 6:10 AM, Pierre Neyron wrote:
> 
> Another question: We figured out that modifying the petitboot of our IBM
> S822LC power8 systems requires reflashing the whole skiroot using a tool
> such as op-test ? Is it correct ? Any advice or pointer to information
> for that task would be very welcome.

Just to mention it, you should be able to boot a petitboot image with
petitboot.  It might make testing easier.

-Geoff