gnu: bootloader: Deprecate "device" field in favor of "target".

* gnu/bootloader.scm (<bootloader-configuration>): Deprecate "device" field in
favor of "target" field.  This is mostly a renaming but also a generalization
to support UEFI targets being paths to a mounted partition instead of a device
name.
* gnu/system/examples/bare-bones.tmpl:
* gnu/system/examples/desktop.tmpl:
* gnu/system/examples/lightweight-desktop.tmpl:
* gnu/system/examples/vm-image.tmpl:
* gnu/system/install.scm:
* gnu/tests.scm:
* gnu/tests/install.scm:
* gnu/tests/nfs.scm:
* tests/system.scm: Adapt all invocations of bootloader-configuration.
* guix/scripts/system.scm (perform-action): Rename device argument to
bootloader-target.
(process-action): Adapt caller.
* doc/guix.texi (Proceeding with the Installation):
* doc/guix.texi (Bootloader Configuration): Update documentation.

gnu: grub-efi-bootloader: Specialize grub-install invocation.

* gnu/bootloader/grub.scm (install-grub-efi): Fix grub-install invocation for
  EFI systems.
* gnu/system/examples/bare-bones.tmpl: Use the newer
"bootloader-configuration" syntax.
* gnu/system/examples/desktop.tmpl: Use bootloader-configuration sytax.  Also,
use the same label for the LUKS-mapped device and the root partition.  Remove
unneeded "title" field for the file-system based on LUKS; as noted in the
manual, the "title" field is ignored for mapped devices.
* gnu/system/examples/lightweight-desktop.tmpl: Use bootloader-configuration,
and use grub-efi-bootloader.

vm: Use grub-hybrid's grub-mkrescue.

* gnu/system/vm.scm (system-disk-image): Use grub-hybrid's grub-mkrescue.
* gnu/bootlader/grub.scm (grub-mkrescue-bootloader): New variable.

system: Add 'grep --color' alias in '.bash_profile' skeleton.

* gnu/system/shadow.scm (default-skeletons)[profile]: Add 'grep' alias.

system: Add a default '.guile' skeleton.

* gnu/system/shadow.scm (default-skeletons): Add ".guile".

vm: Add a <virtual-machine> type and associated gexp compiler.

* gnu/system/vm.scm (system-qemu-image/shared-store-script): Add
 #:options parameter and honor it.
(<virtual-machine>): New record type.
(virtual-machine): New macro.
(port-forwardings->qemu-options, virtual-machine-compiler): New
procedures.

vm: 'iso9660-image' produces a single-file output.

* gnu/system/vm.scm (expression->derivation-in-linux-vm): Add
  #:single-file-output? and pass it to 'load-in-linux-vm'.
(iso9660-image): Pass #:single-file-output? to
'expression->derivation-in-linux-vm'.
* gnu/build/vm.scm (load-in-linux-vm): Add #:single-file-output? and
honor it.

locale: Demonadify the locale creation API.

* gnu/system/locale.scm (single-locale-directory): Use 'computed-file'
instead of 'gexp->derivation'.
(locale-directory): Adjust accordingly and do the same.
* gnu/system.scm (operating-system-directory-base-entries): Adjust
accordingly.

gnu: Remove glibc@2.21 and its traces.

* gnu/packages/base.scm (glibc-2.21): Remove.
* gnu/system/locale.scm (localedef-command)[maybe-version-directory]:
Remove.  Replace call with use of 'package-version'.
(single-locale-directory): Remove 'version>=' conditional.

build, vm: Use a less common label.

* gnu/build/vm.scm (initialize-hard-disk): Use "GuixSD_image" as label.
* gnu/system/install.scm (installation-os): Likewise.
* gnu/system/vm.scm (system-disk-image): Likewise.

gnu: Rename (gnu packages qemu) to (gnu packages virtualization).

* gnu/packages/qemu.scm: Rename this ...
* gnu/packages/virtualization.scm: ... to this.
* gnu/local.mk (GNU_SYSTEM_MODULES),
gnu/packages/bootloaders.scm, gnu/packages/debug.scm,
gnu/packages/gnome.scm, gnu/system/vm.scm,
gnu/tests/install.scm: Adjust accordingly.

system: Refer to native packages when appropriate.

* gnu/system/locale.scm (localedef-command): Use the native LIBC.
* gnu/system/shadow.scm (default-skeletons): Use the native GUILE-WM.

build, vm: Use "GuixSD" or "GUIXSD" as volume label.

* gnu/build/vm.scm (initialize-hard-disk): Use "GuixSD" as label.
* gnu/system/install.scm (installation-os): Use "GuixSD" as label.
* gnu/system/vm.scm (system-disk-image): Use "GuixSD" or "GUIXSD" as volume
label.

Co-authored-by: Ludovic Courtès <ludo@gnu.org>

guix system: Add file system label and uuid to iso9660-image.

* gnu/system/vm.scm (system-disk-image): Pass root-label to ...
(iso9660-image): ... here.  Add keyword arguments #:file-system-label
and #:file-system-uuid.

linux-initrd: Avoid monadic style a bit.

* gnu/system/linux-initrd.scm (expression->initrd): Use 'program-file'
for 'init'.
(flat-linux-module-directory): Use 'computed-file' instead of
'gexp->derivation'.
(raw-initrd): Adjust accordingly.

install: Drop redundant package after c0f5eee4b2cc737be222c4ba331d0.

* gnu/system/install.scm (installation-os): Remove SHADOW.

build: Add iso9660 system image generator.

* build-aux/hydra/gnu-system.scm (qemu-jobs): Add 'iso9660-image .
* gnu/build/vm.scm (make-iso9660-image): New variable.  Export it.
* gnu/system/vm.scm (iso9660-image): New variable.  Use make-iso9660-image.
(system-disk-image): Use iso9660-image.

linux-initrd: Add isofs if necessary.

* gnu/system/linux-initrd.scm (base-initrd): Add isofs.

install: Re-add /bin/sh.

Reported by Divan Santana <divan@santanas.co.za>.
/bin/sh had disappeared in commit
387e175492f960d7d86f34f3b2e43938fa72dbf3.

* gnu/system/install.scm (%installation-services): Add
'special-files-service-type' instance.

vm: Estimate the disk size by default.

* gnu/build/vm.scm (estimated-partition-size): New procedure.
* gnu/system/vm.scm (expression->derivation-in-linux-vm):
Change #:disk-image-size default to 'guess.
[builder]: When DISK-IMAGE-SIZE is 'guess, use
'estimated-partition-size' and compute and estimate of the image size.
(qemu-image): Likewise.
* guix/build/store-copy.scm (file-size, closure-size): New procedures.
* guix/scripts/system.scm (%default-options): Change 'image-size' to
'guess.
* doc/guix.texi (Building the Installation Image): Remove '--image-size'
flag from example.
(Invoking guix system): Document the image size estimate.