build: Use overlayfs instead of unionfs.

Overlayfs is part of the kernel, while unionfs needs FUSE.  This also reduces
the size of the initrd by ca. 4.3% (487K).

* gnu/build/linux-boot.scm (mount-root-file-system): Remove optional parameter
  "unionfs"; mount using overlayfs instead of unionfs; new directory layout
  requied by overlayfs; update documentation.
  [mark-as-not-killable]: Remove now unused function

* gnu/system/linux-initrd.scm (file-system-packages): Remove now unused
  packages "unionfs-fuse/static" and thus unused related 'if'.
  (linux-modules): Replace "fuse" by "overlay".

file-systems: Add support for FAT16.

* gnu/build/file-systems.scm (check-fat32-file-system): Rename to...
(check-fat-file-system): ... this.
(check-file-system): Adjust accordingly.
(fat16-superblock?, read-fat16-superblock)
(fat16-superblock-uuid, fat16-superblock-volume-name): New procedures.
(%partition-label-readers, %partition-uuid-readers): Add FAT16.

file-systems: Preserve UUID types when serializing.

Reported by Roel Janssen <roel@gnu.org>
at <https://lists.gnu.org/archive/html/help-guix/2017-09/msg00094.html>.

* gnu/system/file-systems.scm (file-system->spec): When DEVICE is a
UUID, serialize it in a way that preserves its type.
(spec->file-system): Adjust accordingly.
* gnu/build/file-systems.scm (canonicalize-device-spec): Add case for
when SPEC is 'uuid?'.

file-systems: 'mount-file-system' now takes a <file-system> object.

* gnu/build/file-systems.scm (mount-file-system): Rename 'spec' to 'fs'
and assume it's a <file-system>.
* gnu/build/linux-boot.scm (boot-system): Assume MOUNTS is a list of
<file-system> and adjust accordingly.
* gnu/build/linux-container.scm (mount-file-systems): Remove
'file-system->spec' call.
* gnu/services/base.scm (file-system-shepherd-service): Add
'spec->file-system' call.  Add (gnu system file-systems) to 'modules'.
* gnu/system/linux-initrd.scm (raw-initrd): Use (gnu system
file-systems).  Add 'spec->file-system' call for #:mounts.

activation: Do not create setuid binaries in the store [security fix].

Fixes <https://bugs.gnu.org/28751>.

* gnu/build/activation.scm (activate-setuid-programs)[link-or-copy]: Remove.
Use 'copy-file' instead.

Merge branch 'master' into staging

uuid: Add 'uuid=?' and use it.

* gnu/system/uuid.scm (uuid=?): New procedure.
* tests/uuid.scm ("uuid=?"): New test.
* gnu/build/file-systems.scm (partition-uuid-predicate)
(luks-partition-uuid-predicate): Use it instead of 'bytevector=?'.

Merge branch 'master' into staging

build: Do not store two copies of the ISO-9660 superblock anymore.

* gnu/build/vm.scm (make-iso9660-image): Do not store two copies of the
ISO-9660 superblock anymore.

Merge branch 'master' into staging

file-systems: Introduce (gnu system uuid).

* gnu/build/file-systems.scm (sub-bytevector)
(latin1->string, %fat32-endianness, fat32-uuid->string)
(%iso9660-uuid-rx, string->iso9660-uuid)
(iso9660-uuid->string, %network-byte-order)
(dce-uuid->string, %uuid-rx, string->dce-uuid)
(string->ext2-uuid, string->ext3-uuid, string->ext4-uuid)
(vhashq, %uuid-parsers, %uuid-printers, string->uuid)
(uuid->string): Move to...
* gnu/system/uuid.scm: ... here.  New file.
* gnu/system/file-systems.scm (uuid): Move to the above file.
* gnu/system/vm.scm: Adjust accordingly.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add uuid.scm.

file-systems: Add UUID type dictionaries.

* gnu/build/file-systems.scm (uuid->string): Rename to...
(dce-uuid->string): ... this.
(string->uuid): Rename to...
(string->dce-uuid): ... this.
(vhashq): New macro.
(%uuid-parsers, %uuid-printers): New variables.
(uuid->string, string->uuid): New procedures.

vm: Allow partitions to be initialized with a given UUID.

* gnu/build/vm.scm (<partition>)[uuid]: New field.
(create-ext-file-system): Add #:uuid and honor it.
(create-fat-file-system): Add #:uuid.
(format-partition): Add #:uuid and honor it.
(initialize-partition): Honor the 'uuid' field of PARTITION.

vm: Add comment about deduplication in make-iso9660-image.

* gnu/build/vm.scm (make-iso9660-image): Add comment about the use of
  #:deduplicate #f when calling register-closure.

marionette: 'wait-for-file' can be passed a read procedure.

* gnu/build/marionette.scm (wait-for-file): Add #:read parameter and
honor it.
* gnu/tests/base.scm (run-basic-test)["login on tty1"]: Use
'wait-for-file' instead of inline code.

vm: Create /mnt in the generated ISO image in make-iso9660-image.

This is used in the installation process, as the mountpoint for the target
filesystem.

* gnu/build/vm.scm (make-iso9660-image): Create /mnt within the generated ISO
  image.

vm: Add support for registering closures to make-iso9660-image.

This mimics the functionality in the root-partition-initializer used in
creating the QEMU image. This helps when trying to run guix system init from
the generated ISO image.

* gnu/build/vm.scm (make-iso9660-image): Add support for registering closures.

Merge branch 'master' into staging

marionette: Augment the set of keystrokes.

* gnu/build/marionette.scm (%qwerty-us-keystrokes): Add ', ", and `.

marionette: Fix typing of capital letters.

Previously we'd use "sendkey P" instead of "sendkey shift-p", which had
no effect.

* gnu/build/marionette.scm (character->keystroke): New procedure.
(string->keystroke-commands): Use it.