This change removes the documentation to copy master_grub_cfg.txt to
/tftpboot/grub/grub.cfg and instead writes it on conductor startup.
This grub config is a simple redirect config requested by grub network
boot. "master" has been renamed to "initial" as a more accurate label
of its function.
New configuration option [pxe]initial_grub_template allows the deployer
to specify a different initial grub template.
Change-Id: I71191dd399a6c49607f91d69b5b1673799a38624
3f76724dfb