Use 'targets' instead of the now-deprecated 'target' field.

* build-node.scm <bootloader-configuration>: Use 'targets' instead of
'target'.
* guix-hpc1.scm, guix-hpc3.scm, head-node.scm: Likewise.

build-node.scm

@@ -44,7 +44,7 @@
 
   (bootloader (bootloader-configuration
                (bootloader grub-efi-bootloader)
-               (target "/boot/efi")))
+               (targets '("/boot/efi"))))
 
   (file-systems %base-file-systems)   ;must be configured through inheritance
 

guix-hpc1.scm

@@ -10,7 +10,7 @@
     ;; This is a non-EFI setup.
     (bootloader (bootloader-configuration
                  (bootloader grub-bootloader)
-                 (target "/dev/sda")))
+                 (targets '("/dev/sda"))))
 
     (initrd-modules (append (list "megaraid_sas")
                             %base-initrd-modules))

guix-hpc3.scm

@@ -10,7 +10,7 @@
     ;; This is a UEFI setup.
     (bootloader (bootloader-configuration
                  (bootloader grub-efi-bootloader)
-                 (target "/boot/efi")))
+                 (targets '("/boot/efi"))))
 
     (initrd-modules (append (list "megaraid_sas")
                             %base-initrd-modules))

head-node.scm

@@ -234,7 +234,7 @@
 
   (bootloader (bootloader-configuration
                (bootloader grub-efi-bootloader)
-               (target "/boot/efi")))
+               (targets '("/boot/efi"))))
 
   ;; sudo mdadm --create /dev/md0 --level raid10 --raid-disks 4 -p f2 /dev/sd[ab]2