Revert "grub: Allow setting the boot root explicitly"

This reverts commit e4630c1d41d513eb709bddb39043da84442235a7.
Update grub 2.00 to 2.02-beta2
Add optional zfsSupport to the nixos grub configuration
Enable grub zfsSupport if zfs is built into the initrd
Update the grub configuration script to handle more complex filesystem layouts including full zfs / and /boot
grub: Add support for forcing devices to be identified with labels or  UUIDs
grub: Add support for detecting btrfs subvolumes
nixos/grub: Fix some silly perl struct accesses
nixos/grub: Fix typo
grub: Build grub2 from git instead of using the unpredictable generated tarball
nixos/grub: Refactor perl script to remove the Switch module
nixos/grub: Refactor install-grub.pl and correct perl syntax
nixos/grub: Catch errors from command execution
nixos/release: Dynamically generate installer tests
grub: Change fsIdentifier to str from string
tests/installer: Add btrfs tests for grub and nixos-generate-config
tests/installer: Test for more grub configurations
installer/btrfs: Typo in subvol
nixos/grub: Needs mount so add utillinux to bin
tests/installer: fix mount