vm: Use the 'umount' procedure instead of util-linux's 'umount' command.

* gnu/build/vm.scm (initialize-root-partition, initialize-hard-disk): Use the
  'umount' procedure instead of invoking the 'umount' command.
* gnu/system/vm.scm (qemu-image): Remove UTIL-LINUX from INPUTS.

gnu/build/vm.scm

@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2013, 2014 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2013, 2014, 2015 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -172,7 +172,7 @@ volume name."
                                   (string-append "/xchg/" closure)))
               closures)
     (unless copy-closures?
-      (system* "umount" target-store)))
+      (umount target-store)))
 
   ;; Add the non-store directories and files.
   (display "populating...\n")
@@ -236,6 +236,6 @@ SYSTEM-DIRECTORY is the name of the directory of the 'system' derivation."
   (unless register-closures?
     (reset-timestamps target-directory))
 
-  (zero? (system* "umount" target-directory)))
+  (umount target-directory))
 
 ;;; vm.scm ends here

gnu/system/vm.scm

@@ -212,7 +212,7 @@ the image."
                     (guix build utils))
 
        (let ((inputs
-              '#$(append (list qemu parted grub e2fsprogs util-linux)
+              '#$(append (list qemu parted grub e2fsprogs)
                          (map canonical-package
                               (list sed grep coreutils findutils gawk))
                          (if register-closures? (list guix) '())))