Make --bootloader=grub2 set debug instead of single in grub.cfg

gen_bootloader.sh

@@ -51,6 +51,7 @@ set_bootloader_grub2() {
 	print_info 1 "You can customize Grub2 parameters in /etc/default/grub."
 	print_info 1 "Running grub2-mkconfig to create ${GRUB_CONF}..."
 	grub2-mkconfig -o "${GRUB_CONF}"
+	[ "${BUILD_RAMDISK}" -ne 0 ] && sed -i 's/ro single/ro debug/' "${GRUB_CONF}"
 }
 
 set_bootloader_grub() {