Support gPXE in boot.py
Support gPXE in boot.py

Some machines have gPXE burned into the NIC ROM, and can kickstart via
HTTP without having to chainload iPXE. Adapted from FGI netboot.py.

CSC-IT-Center-for-Science/ansible-role-pxe_bootstrap,CSC-IT-Center-for-Science/ansible-role-pxe_bootstrap