gnu: guix: Update to 0.4.

* gnu/packages/package-management.scm (guix): Update to 0.4.
  (guix-0.4): Remove.
* gnu/system/vm.scm (qemu-image, system-qemu-image): Use GUIX instead of
  GUIX-0.4.

gnu: vm: Remove erroneous store reference.

* gnu/system/vm.scm (system-qemu-image): Remove reference from BOOT to
  MINGETTY since MINGETTY may not be valid yet.

gnu: vm: Add more packages to the profile.

* gnu/system/vm.scm (system-qemu-image): Add grep, sed, and Findutils to
  the profile.

gnu: vm: Add a few packages to the default profile.

* gnu/system/vm.scm (system-qemu-image): Add procps, psmisc, and Zile to
  the default profile.  Increase the image size to 550 MiB.

gnu: dmd: Make the 'networking' service slightly more robust.

* gnu/system/dmd.scm (static-networking-service)[start]: Sleep before
  running 'route', to leave time for the interface to come up.
  [stop]: Run "route del -net default".

gnu: vm: Set the right permissions and ownership on directories.

* gnu/system/vm.scm (qemu-image): Change the store's mode to #o1775.
  Support 'populate' clauses that specify a UID and GID.
  (system-qemu-image): Make sure /nix/store has owner 'root' and group
  'guixbuild'.  Set the right owner for /home/guest.  Create
  /var/nix/profiles/per-user/{root,guest}.

gnu: vm: Add build users.

* gnu/system/shadow.scm (guix-build-accounts): New procedure.
* gnu/system/vm.scm (system-qemu-image): Use it.  Add the "guixbuild"
  group.
* gnu/system/dmd.scm (guix-service): Add 'builder-group' parameter.
  Pass 'guix-daemon' the '--build-users-group' option.

gnu: vm: Add /etc/{services,protocols,rpc} to the image.

* gnu/system/vm.scm (system-qemu-image): Link
  /etc/{services,protocols,rpc}.  Add net-base as an input.

gnu: vm: Add a 'guest' account.

* gnu/system/vm.scm (system-qemu-image): Add a "guest" user and a
  "users" user group.  Make /home/guest.  Add /etc/group.  Update
  /etc/issue to mention it.

gnu: shadow: Add record type for user groups.

* gnu/system/shadow.scm (<user-group>): New record type.
  (group-file): New procedure.
* gnu/system/vm.scm (system-qemu-image): Use it.

gnu: shadow: Add record type for user accounts.

* gnu/system/shadow.scm (<user-account>): New record type.
  (passwd-file): Use it.
* gnu/system/vm.scm (system-qemu-image): Adjust accordingly.

gnu: vm: Set the default networking route.

* gnu/system/dmd.scm (static-networking-service): Add #:gateway
  parameter and honor it.
* gnu/system/vm.scm (system-qemu-image): Pass #:gateway to
  'static-networking-service'.

Merge branch 'master' into core-updates

gnu: vm: Add nscd service.

* gnu/system/dmd.scm (nscd-service): New procedure.
* gnu/system/vm.scm (system-qemu-image): Use it.  Make /var/run/nscd.

gnu: vm: Add 'networking' service.

* gnu/system/vm.scm (system-qemu-image): Use
  'static-networking-service'.  Add /etc/resolv.conf.  Add Inetutils to
  the profile.
* gnu/system/dmd.scm (static-networking-service): New procedure.

gnu: vm: Register the profile as a GC root.

* gnu/system/vm.scm (system-qemu-image): Register PROFILE as a GC root.

gnu: vm: Add 'host-name' service.

* gnu/system/dmd.scm (host-name-service): New procedure.
  (mingetty-service): Require the 'host-name' service.
* gnu/system/vm.scm (system-qemu-image): Add the 'host-name' service.
  Set PS1 in /etc/bashrc to something sensible.

gnu: vm: Add /etc/issue and a motd.

* gnu/system/vm.scm (system-qemu-image): Build a 'motd' and an 'issue'
  file.  Pass 'unix-pam-service' that motd.  Have /etc/issue point to
  the 'issue' file.

gnu: vm: Change #:populate to a list of directives.

* gnu/system/vm.scm (qemu-image): Change 'populate' parameter to be a
  list of directives.
  (system-qemu-image): Adjust accordingly.

gnu: vm: Add more ttys.

* gnu/system/vm.scm (system-qemu-image): Add more ttys.