bootloader: Adapt vm to new bootloader API.

* gnu/build/install.scm (install-boot-config): New procedure.
  (install-grub): Move to (gnu bootloader grub).
* gnu/build/vm.scm (register-bootcfg-root): Rename register-grub.cfg-root and
  adjust accordingly.
  (initialize-hard-disk): Takes a bootloader-package, bootcfg, bootcfg-location and
  bootloader-installer procedure. Adjust accordingly.
* gnu/system/vm.scm (qemu-image): Adjust to initialize-hard-disk.
  (system-disk-image, system-qemu-image, system-qemu-image/shared-store):
  Adjust to qemu-image.

bootloader: Add extlinux support.

* gnu/bootloader.scm: New file.
* gnu/bootloader/extlinux.scm: New file.
* gnu/bootloader/grub.scm: New file.
* gnu/local.mk: Build new files.
* gnu/system.scm: Adapt to new bootloader api.
* gnu/scripts/system.scm: Adapt to new bootloader api.
* gnu.scm: Remove (gnu system grub) and replace by (gnu bootloader) and (gnu
bootloader grub) modules.
* gnu/system/grub.scm: Moved content to gnu/bootloader/grub.scm.
* gnu/system/vm: Replace (gnu system grub) module by (gnu bootloader).
* gnu/tests.scm: Ditto.
* gnu/tests/nfs.scm: Ditto.

system: grub: Actually default to 'gfxterm' for displaying the GRUB menu.

This is a followup to commit e0b2e93005188ab4d6c7413a27832ba2fb7388e8.

* gnu/system/grub.scm (eye-candy): Re-order the elements of the generated
GRUB configuration.

system: grub: Expose GRUB's interactive interface settings.

* gnu/system/grub.scm (<grub-configuration>): Add new fields
terminal-outputs, terminal-inputs, serial-unit, and serial-speed.
(grub-setup-io, setup-gfxterm): New procedures.
* doc/guix.texi (GRUB Configuration): Document the new fields.

system: grub: Use the native Guile-Cairo and Guile-SVG.

* gnu/system/grub.scm (svg->png): Use 'ungexp-native' aka. #+ when
referring to GUILE-CAIRO, GUILE-SVG, and SVG.

system: Allow root to run "su" without password.

* gnu/system/pam.scm (unix-pam-service): Add pam-entry for "pam_rootok.so" to
auth field when ALLOW-ROOT? is #T.
(base-pam-services): Allow root to run "su" without authentication.

system: grub: Use boot-parameters instead of menu-entry where possible.

* gnu/system/grub.scm (boot-parameters->menu-entry): New variable.
(grub-configuration-file): Use boot-parameters
instead of menu-entry where possible.
* guix/scripts/system.scm (profile-boot-parameters): Update docstring.
(reinstall-grub): Use profile-boot-parameters.
(perform-action): Use profile-boot-parameters.

system: vm: Use operating-system-kernel-arguments.

* gnu/system/vm.scm (system-qemu-image/shared-store-script):
Use operating-system-kernel-arguments.

ui: Rename '_' to 'G_'.

This avoids collisions with '_' when the latter is used as a 'match'
pattern for instance.  See
<https://lists.gnu.org/archive/html/guix-devel/2017-04/msg00464.html>.

* guix/ui.scm: Rename '_' to 'G_'.
* po/guix/Makevars (XGETTEXT_OPTIONS): Adjust accordingly.
* build-aux/compile-all.scm (warnings): Remove 'format'.
* gnu/packages.scm,
gnu/services.scm,
gnu/services/shepherd.scm,
gnu/system.scm,
gnu/system/shadow.scm,
guix/gnupg.scm,
guix/http-client.scm,
guix/import/cpan.scm,
guix/import/elpa.scm,
guix/import/pypi.scm,
guix/nar.scm,
guix/scripts.scm,
guix/scripts/archive.scm,
guix/scripts/authenticate.scm,
guix/scripts/build.scm,
guix/scripts/challenge.scm,
guix/scripts/container.scm,
guix/scripts/container/exec.scm,
guix/scripts/copy.scm,
guix/scripts/download.scm,
guix/scripts/edit.scm,
guix/scripts/environment.scm,
guix/scripts/gc.scm,
guix/scripts/graph.scm,
guix/scripts/hash.scm,
guix/scripts/import.scm,
guix/scripts/import/cpan.scm,
guix/scripts/import/cran.scm,
guix/scripts/import/crate.scm,
guix/scripts/import/elpa.scm,
guix/scripts/import/gem.scm,
guix/scripts/import/gnu.scm,
guix/scripts/import/hackage.scm,
guix/scripts/import/nix.scm,
guix/scripts/import/pypi.scm,
guix/scripts/import/stackage.scm,
guix/scripts/lint.scm,
guix/scripts/offload.scm,
guix/scripts/pack.scm,
guix/scripts/package.scm,
guix/scripts/perform-download.scm,
guix/scripts/publish.scm,
guix/scripts/pull.scm,
guix/scripts/refresh.scm,
guix/scripts/size.scm,
guix/scripts/substitute.scm,
guix/scripts/system.scm,
guix/ssh.scm,
guix/upstream.scm: Use 'G_' instead of '_'.  Most of this change was
obtained by running: "sed -i -e's/(_ "/(G_ "/g' `find -name \*.scm`".

Merge branch 'master' into staging

system: Rename operating-system-kernel-arguments to operating-system-user-kernel-arguments.

* gnu/system.scm (operating-system-kernel-arguments): Rename to ...
(operating-system-user-kernel-arguments): ... this.
(<operating-system>): Adapt accordingly.
(operating-system-bootcfg): Adapt accordingly.
(operating-system-parameters-file): Adapt accordingly.
* gnu/system/vm.scm (system-qemu-image/shared-store-script): Adapt
accordingly.

Merge branch 'master' into staging

system: Make grub use <menu-entry> instead of <boot-parameters> again.

* gnu/system/grub.scm: Remove boot-parameters->menu-entry.
(grub-configuration): Don't use boot-parameters->menu-entry.
* gnu/system.scm (operating-system-bootcfg): Use menu-entry.
* guix/scripts/system.scm (reinstall-grub): Use profile-grub-entries.
(perform-action): Use profile-grub-entries.

system: Pass boot-parameters to (gnu system grub).

* gnu/system.scm (operating-system-bootcfg): Pass boot-parameters.
* gnu/system/grub.scm (boot-parameters->menu-entry): New variable.
(grub-configuration-file): Use boot-parameters->menu-entry.

Signed-off-by: Danny Milosavljevic <dannym@scratchpost.org>

system: grub: Use (first all-entries) instead of (first entries).

* gnu/system/grub.scm (grub-configuration-file): Use (first all-entries)
instead of (first entries).

vm: Reword grub.cfg to bootcfg.

* gnu/build/vm.scm (register-grub.cfg-root): Reword grub.cfg to bootcfg,
(initialize-hard-disk): ditto,
* gnu/system/vm.scm (system-disk-image): ditto,
(system-qemu-image): ditto,
(system-qemu-image/shared-store): ditto.

Signed-off-by: Danny Milosavljevic <dannym@scratchpost.org>

system: Rename operating-system-grub.cfg to operating-system-bootcfg.

* gnu/system.scm (operating-system-grub.cfg): Rename to...
(operating-system-bootcfg): ... this.
* gnu/system/vm.scm (system-disk-image): Use operating-system-bootcfg.
(system-qemu-image): Use operating-system-bootcfg.
(system-qemu-image/shared-store): Use operating-system-bootcfg.
* guix/scripts/system.scm (perform-action): Use operating-system-bootcfg.

Signed-off-by: Danny Milosavljevic <dannym@scratchpost.org>

Merge branch 'master' into staging

doc: Use OpenSSH instead of lsh in bare-bones template.

* gnu/system/examples/bare-bones.tmpl (services): Use openssh-service-type
instead of lsh-service.

Merge branch 'master' into core-updates