accounts: Add default value for the 'home-directory' field of <user-account>.

* gnu/system/accounts.scm (<user-account>)[home-directory]: Mark as
thunked and add a default value.
(default-home-directory): New procedure.
* doc/guix.texi (User Accounts): Remove 'home-directory' from example.
* gnu/system/examples/bare-bones.tmpl: Likewise.
* gnu/system/examples/beaglebone-black.tmpl: Likewise.
* gnu/system/examples/desktop.tmpl: Likewise.
* gnu/system/examples/docker-image.tmpl: Likewise.
* gnu/system/examples/lightweight-desktop.tmpl: Likewise.
* gnu/system/install.scm (installation-os): Likewise.
* gnu/tests.scm (%simple-os): Likewise.
* gnu/tests/install.scm (%minimal-os, %minimal-os-on-vda):
(%separate-home-os, %encrypted-root-os, %btrfs-root-os): Likewise.
* tests/accounts.scm ("allocate-passwd")
("allocate-passwd with previous state"): Likewise.

1 files changed, 2 insertions, 3 deletions

diff --git a/gnu/tests.scm b/gnu/tests.scm
index 9e8eed7d950..0871b4c6f77 100644
--- a/gnu/tests.scm
+++ b/gnu/tests.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2016, 2017, 2018 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2016, 2017, 2018, 2019 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2017 Mathieu Othacehe <m.othacehe@gmail.com>
 ;;; Copyright © 2017 Tobias Geerinckx-Rice <me@tobias.gr>
 ;;;
@@ -219,8 +219,7 @@ the system under test."
                   (name "alice")
                   (comment "Bob's sister")
                   (group "users")
-                  (supplementary-groups '("wheel" "audio" "video"))
-                  (home-directory "/home/alice"))
+                  (supplementary-groups '("wheel" "audio" "video")))
                  %base-user-accounts))))
 
 (define-syntax-rule (simple-operating-system user-services ...)