gnu: sudo: Use /var/run/sudo instead of /run/sudo.

* gnu/packages/admin.scm (sudo)[arguments]: Pass
--with-rundir=/var/run/sudo since /var/run is cleaned up at boot time on
GuixSD whereas /run is not.

gnu/packages/admin.scm

@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2012, 2013, 2014, 2015 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2012, 2013, 2014, 2015, 2016 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2013 Cyril Roelandt <tipecaml@gmail.com>
 ;;; Copyright © 2014, 2015 Mark H Weaver <mhw@netris.org>
 ;;; Copyright © 2014, 2015 Eric Bavier <bavier@member.fsf.org>
@@ -705,7 +705,7 @@ system administrator.")
     (arguments
      `(#:configure-flags
        (list "--with-logpath=/var/log/sudo.log"
-             "--with-rundir=/run/sudo"
+             "--with-rundir=/var/run/sudo"    ;must be cleaned up at boot time
              "--with-vardir=/var/db/sudo"
              "--with-iologdir=/var/log/sudo-io"