build/init:
 - fix /etc/default/grub manipulation (it was broken by commit 94ba6af73531fc591c66f5e6a48b47fc23093221)
 - add support for cloud-init for RHEL/CentOS (to be tested)
 - request localboot from pxemngr at the right time
server/upload.py:
 - do not call pxemngr for localboot instead pass a variable to let init do it