* gnu/bootloader/extlinux.scm (extlinux-configuration-file): Remove
mentions of "GuixSD".
* gnu/bootloader/grub.scm (install-grub-efi): Likewise.
* gnu/build/vm.scm (make-iso9660-image): Change default #:volume-id to
"Guix_image".
(initialize-hard-disk): Search for the "Guix_image" label.
* gnu/ci.scm (system-test-jobs, tarball-jobs): Remove "GuixSD".
* gnu/installer/newt/welcome.scm (run-welcome-page): Likewise.
* gnu/packages/audio.scm (supercollider)[description]: Likewise.
* gnu/packages/curl.scm (curl): Likewise.
* gnu/packages/emacs.scm (emacs): Likewise.
* gnu/packages/gnome.scm (network-manager): Likewise.
* gnu/packages/julia.scm (julia): Likewise.
* gnu/packages/linux.scm (alsa-plugins): Likewise.
(powertop, wireless-regdb): Likewise.
* gnu/packages/package-management.scm (guix): Likewise.
* gnu/packages/polkit.scm (polkit): Likewise.
* gnu/packages/tex.scm (texlive-bin): Likewise.
* gnu/services/base.scm (file-systems->fstab): Likewise.
* gnu/services/cups.scm (%cups-activation): Likewise.
* gnu/services/mail.scm (%dovecot-activation): Likewise.
* gnu/services/messaging.scm (prosody-configuration)[log]: Likewise.
* gnu/system/examples/vm-image.tmpl (vm-image-motd): Likewise.
* gnu/system/install.scm (installation-os)[file-systems]: Change root
file system label to "Guix_image".
* gnu/system/mapped-devices.scm (check-device-initrd-modules):
Remove "GuixSD".
* gnu/system/vm.scm (system-docker-image): Likewise.
(system-disk-image)[root-label]: Change to "Guix_image".
* gnu/tests/install.scm (run-install): Remove "GuixSD".
* guix/modules.scm (guix-module-name?): Likewise.
* nix/libstore/optimise-store.cc: Likewise.

* gnu/ci.scm (system-test-jobs): Return the empty list when SYSTEM is
"armhf-linux".

This fixes a regression introduced in
b5f8c2c88543158e8aca76aa98f9009f6b9e743a whereby 'current-guix' (needed
by some of the system tests) would fail to build.
Reported by Ricardo Wurmus <rekado@elephly.net>.

It also speeds up compilation of 'current-guix' since the channel
instance is already compiled or can be built quickly compared to the
default 'current-guix'.

* gnu/packages/package-management.scm (current-guix-package): New
variable.
(current-guix): Honor it.
* gnu/ci.scm (channel-build-system): New variable.
(channel-instances->derivation): New procedure.
(system-test-jobs): Add #:source and #:commit parameters.
Define 'instance' and parameterize CURRENT-GUIX-PACKAGE.
(hydra-jobs)[checkout, commit, source]: New variables.
Pass #:source and #:commit to 'system-test-jobs'.

Previously we would rely on auto-compilation of all the Guix modules.
The complete evaluation would take ~15mn on berlin.guixsd.org and
require lots of RAM.  This approach should be faster since potentially
only part of the modules are rebuilt.  Furthermore, as a side-effect, it
builds the derivations that 'guix pull' uses.

* build-aux/hydra/gnu-system.scm: Remove 'eval-when' form.
(hydra-jobs): New procedure.
* gnu/ci.scm (package->alist, qemu-jobs, system-test-jobs)
(tarball-jobs): Return strings for the 'license' field.
* guix/self.scm (compiled-guix)[*cli-modules*]: Add (gnu ci).

* build-aux/hydra/gnu-system.scm: Move code to...
* gnu/ci.scm: ... here.  New file.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add it.