install: Use udev.

* gnu/system/install.scm (installation-services): Call 'udev-service'.

system: Use the default 'groups' field.

* gnu/system/install.scm (installation-os): Remove 'groups' field.
* build-aux/hydra/demo-os.scm: Likewise.

system: Remove useless 'members' field of 'user-group'.

* gnu/system/shadow.scm (<user-group>)[members]: Remove field.
* gnu/system/install.scm (installation-os)[users]: Remove 'members'
  fields.  Use 'supplementary-groups' for 'guest'.
* build-aux/hydra/demo-os.scm (users): Likewise.
* gnu/services/base.scm (guix-service): Remove 'members' field.

Merge branch 'master' into core-updates

install: Add missing argv[0] in Info invocation.

* gnu/system/install.scm (log-to-info): Add "info" as second argument to
  'execl'.

install: Register the hydra.gnu.org key on the installation image.

* gnu/services/base.scm (hydra-key-authorization): New procedure.
  (guix-service): Add #:authorize-hydra-key? parameter; honor it using
  'hydra-key-authorization'.
* gnu/system/install.scm (installation-services): Pass
  #:authorize-hydra-key? #t.

system: Define '%base-packages' and use it.

* gnu/system.scm (<operating-system>)[packages]: Change default value to
  %BASE-PACKAGES.
  (%base-packages): New variable.
* gnu/system/install.scm (installation-os): Use it when defining the
  'packages' field.
* doc/guix.texi (Using the Configuration System): Use %BASE-PACKAGES in
  example.  Remove now unneeded module imports.  Explain this.

install: Add more useful packages.

* gnu/system/install.scm (installation-os)[packages]: Add isc-dhcp,
  net-tools, ddrescue, kbd, and texinfo-4.

gnu: Merge Parted, fdisk, and ddrescue in (gnu packages disk).

* gnu/packages/parted.scm: Rename to...
* gnu/packages/disk.scm: ... this.  New file.  Merge with...
* gnu/packages/fdisk.scm: ... this; remove file;
* gnu/packages/ddrescue.scm: ... and this; remove file.
* gnu/system/install.scm, gnu/system/vm.scm: Adjust accordingly.
* gnu-system.am (GNU_SYSTEM_MODULES): Remove
  gnu/packages/{parted,fdisk,ddrescue}.scm and add
  gnu/packages/disk.scm.

Add (gnu system install).

* gnu/system/install.scm: New file.
* gnu-system.am (GNU_SYSTEM_MODULES): Add it.