wic: isoimage-isohybrid: add grubefi configfile support
The latest wic kickstart refactoring introduced a bootloader option
"--configfile" which lets wks' specify a custom grub.cfg for use
while booting. This is very useful for creating stuff like boot menus.
This change lets isoimage-isohybrid use --configfile; if this option is
not specified in a wks, it generates a default cfg as before.
Signed-off-by: Ioan-Adrian Ratiu <adrian.ratiu@ni.com> Signed-off-by: Ross Burton <ross.burton@intel.com>
