':' is currently used as separator in /boot/grub/state for the list of
devices GRUB should be installed to. The problem is that ':' itself may
appear in a device path:
/dev/disk/by-id/usb-SanDisk_Cruzer_20043512300546C0B317-0:0
With such a path, NixOS will install GRUB *every* time, because it
thinks the configuration differs from the state file (due to the wrong
list split). Fix it by using ',' as separator.
For existing systems with GRUB installed on multiple devices, this
change means that GRUB will be installed one extra time.
aeb516c741