[CentOS] 7.2 installer says "/dev/root does not exist"

Wed Apr 13 20:47:10 UTC 2016
Anand Buddhdev <anandb at ripe.net>

Hi folks,

I have an existing CentOS 7.2 system, that I want to re-install. I
copied /vmlinuz and /initrd.img into /boot, place my kickstart file into
/boot, and created a grub2 menu entry for this, as follows:

menuentry "Install CentOS 7" {
    insmod gzio
    insmod part_gpt
    insmod xfs
    set root=(hd0,2)
    linux /vmlinuz console=tty0 console=ttyS1,115200
    initrd /initrd.img

When I reboot and select this, the kernel boots, unpacks the initrd, and
then exits with the warning "/dev/root" does not exist.

What am I doing wrong? I thought this would be enough to get the
installer to run and re-install the system from my kickstart file.