Refactor constants referring to sizes (remove suffix)

Keeping the prefix in the constant in the constant value makes arithmetic ugly (since the prefix needs to be stripped).

For consistency, all the constants using this format have had the same treatment applied. There's an argument for leaving their format inconsistent, but I prefer not to.

install-zfs.sh

@@ -46,14 +46,14 @@ v_suitable_disks=()          # (/dev/by-id/disk_id, ...); scope: find_suitable_d
 # Note that Linux Mint is "Linuxmint" from v20 onwards. This actually helps, since some operations are
 # specific to it.
 
-c_efi_system_partition_size=512M
-c_default_boot_partition_size=2048M
+c_efi_system_partition_size=512 # megabytes
+c_default_boot_partition_size=2048 # megabytes
 c_default_bpool_tweaks="-o ashift=12"
 c_default_rpool_tweaks="-o ashift=12 -O acltype=posixacl -O compression=lz4 -O dnodesize=auto -O relatime=on -O xattr=sa -O normalization=formD"
 c_zfs_mount_dir=/mnt
 c_installed_os_data_mount_dir=/target
 declare -A c_supported_linux_distributions=([Debian]=10 [Ubuntu]="18.04 20.04" [UbuntuServer]="18.04 20.04" [LinuxMint]="19.1 19.2 19.3" [Linuxmint]="20" [elementary]=5.1)
-c_temporary_volume_size=12G  # large enough; Debian, for example, takes ~8 GiB.
+c_temporary_volume_size=12  # gigabytes; large enough - Debian, for example, takes ~8 GiB.
 c_passphrase_named_pipe=$(dirname "$(mktemp)")/zfs-installer.pp.fifo
 c_passphrase_named_pipe_2=$(dirname "$(mktemp)")/zfs-installer.pp.2.fifo
 
@@ -170,7 +170,7 @@ The procedure can be entirely automated via environment variables:
 
 - ZFS_OS_INSTALLATION_SCRIPT : path of a script to execute instead of Ubiquity (see dedicated section below)
 - ZFS_SELECTED_DISKS         : full path of the devices to create the pool on, comma-separated
-- ZFS_BOOT_PARTITION_SIZE    : integer number with `M` or `G` suffix (defaults to `'$c_default_boot_partition_size'`)
+- ZFS_BOOT_PARTITION_SIZE    : integer number with `M` or `G` suffix (defaults to `'${c_default_boot_partition_size}M'`)
 - ZFS_ENCRYPT_RPOOL          : set 1 to encrypt the pool
 - ZFS_PASSPHRASE             : set non-blank to encrypt the pool, and blank not to. if unset, it will be asked.
 - ZFS_DEBIAN_ROOT_PASSWORD
@@ -556,7 +556,7 @@ function ask_boot_partition_size {
     while [[ ! $v_boot_partition_size =~ ^[0-9]+[MGmg]$ ]]; do
       v_boot_partition_size=$(whiptail --inputbox "${boot_partition_size_invalid_message}Enter the boot partition size.
 
-Supported formats: '512M', '3G'" 30 100 $c_default_boot_partition_size 3>&1 1>&2 2>&3)
+Supported formats: '512M', '3G'" 30 100 ${c_default_boot_partition_size}M 3>&1 1>&2 2>&3)
 
       boot_partition_size_invalid_message="Invalid boot partition size! "
     done
@@ -756,7 +756,7 @@ function install_host_packages_UbuntuServer {
 function setup_partitions {
   print_step_info_header
 
-  local temporary_partition_start=-$((${c_temporary_volume_size:0:-1} + v_free_tail_space))G
+  local temporary_partition_start=-$((c_temporary_volume_size + v_free_tail_space))G
 
   if [[ $v_free_tail_space -eq 0 ]]; then
     local tail_space_start=0
@@ -775,10 +775,10 @@ function setup_partitions {
     #
     wipefs --all "$selected_disk"
 
-    sgdisk -n1:1M:+"$c_efi_system_partition_size" -t1:EF00 "$selected_disk" # EFI boot
-    sgdisk -n2:0:+"$v_boot_partition_size"        -t2:BF01 "$selected_disk" # Boot pool
-    sgdisk -n3:0:"$temporary_partition_start"     -t3:BF01 "$selected_disk" # Root pool
-    sgdisk -n4:0:"$tail_space_start"              -t4:8300 "$selected_disk" # Temporary partition
+    sgdisk -n1:1M:+"${c_efi_system_partition_size}M" -t1:EF00 "$selected_disk" # EFI boot
+    sgdisk -n2:0:+"$v_boot_partition_size"           -t2:BF01 "$selected_disk" # Boot pool
+    sgdisk -n3:0:"$temporary_partition_start"        -t3:BF01 "$selected_disk" # Root pool
+    sgdisk -n4:0:"$tail_space_start"                 -t4:8300 "$selected_disk" # Temporary partition
   done
 
   # The partition symlinks are not immediately created, so we wait.