Automated install using preesed – grub confirmation message issue

I am performing an automated install of a custom ubuntu 14.04 server using a combination of preseed and kickstart methods. Everything is fine except the annoying grub confirmation message as shown below:

The kickstart file:

#Generated by Kickstart Configurator
#platform=AMD64 or Intel EM64T

#System language
lang en_US
#Language modules to install
langsupport en_US
#System keyboard
keyboard us
#System mouse
mouse
#System timezone
timezone Asia/Tokyo
#Root password
rootpw --disabled
#Initial user
user ubuntu --fullname "ubuntu" --iscrypted --password xxx
#Reboot after installation
reboot
#Use text mode install
text
#Install OS instead of upgrade
install
#Use CDROM installation media
cdrom
#System bootloader configuration
bootloader --location=mbr 
#Clear the Master Boot Record
zerombr yes
#Partition clearing information
clearpart --all --initlabel 
#System authorization infomation
auth  --useshadow  --enablemd5 
#Firewall configuration
firewall --enabled 
#Do not configure the X Window System
skipx

The preseed file:

d-i preseed/early_command string umount /media
d-i partman/confirm_write_new_label boolean true
d-i partman/choose_partition \
select Finish partitioning and write changes to disk
d-i partman/confirm boolean true

This is the output of debconf-show grub-pc after installation:

Any ideas on avoiding this message and make the installation fully automated. Thanks in advance.

Edit:
This is my current preseed file:

d-i partman/confirm_write_new_label boolean true
d-i partman/choose_partition \
select Finish partitioning and write changes to disk
d-i partman/confirm boolean true
d-i grub-installer/only_debian boolean true
d-i grub-installer/timeout  string 2

Answer

d-i grub-installer/only_debian boolean true
d-i grub-installer/timeout  string 2

Attribution
Source : Link , Question Author : Vijay47 , Answer Author : Gerald Schneider