Use blkid or e2label /dev/sda1 to get the partition label then replace it in your fstab, the root option in grub.cfg file is different, it is used to set the root file system.
Add the following lines to your /etc/defaut/grub :
GRUB_DISABLE_LINUX_UUID=true
GRUB_ENABLE_LINUX_LABEL=true
Then edit the 2 lines in your /boot/grub/grub.cfg as follows:
search --no-floppy --label root --set=root
linux /boot/vmlinuz-4.9.0-3-amd64 root=LABEL=root ro single