Bug#865141: update-grub fails to properly update grub.cfg after vgrename

[Grant Chesy]

Package: grub-pc
Version: 2.02~beta3-5

The following works on Jessie (2.02~beta2-22+deb8u), but fails to work 
on Stretch (2.02~beta3-5):

vgrename /dev/vg_oldname vg_newname
sed -i'.bak' s/vg_oldname/vg_newname/g' /etc/fstab
update-initramfs -u
update-grub

On Stretch, the old vg name does not get updated to the new name in 
grub.cfg, and the host fails to boot.


A temporary work around is to manually update /boot/grub/grub.cfg after 
a vgrename:

sed -i'.bak' s/vg_oldname/vg_newname/g' /boot/grub/grub.cfg