Hello, Neil.
Thank You for replay. I have seen all links mentioned by You but I was not smart enough to understand what fields exists and what I could change/add/remove.
So I've started to look inside 'x86.jinja2' and sources of 'lava-dispatcher'. I think it would be possible to add my testing as computer of 'x86' device type. All I need to understand is how to setup iPXE, TFTP, DHCP (maybe something else) to get it working. Do You know about that device type and its usage?