package/util-linux: add uuidd user and group

When util-linux is compiled with the uuidd daemon and with systemd
init, the rootfs creation fails in fakeroot as follows:

    printf 'host/bin/systemctl --root=build/buildroot-fs/ext2/target preset-all\n' >> build/buildroot-fs/ext2/fakeroot
    [...]
    FAKEROOTDONTTRYCHOWN=1 host/bin/fakeroot -- build/buildroot-fs/ext2/fakeroot
    rootdir=build/buildroot-fs/ext2/target
    table='build/buildroot-fs/full_devices_table.txt'
    ignored spec: h /var/log/journal/%m - - - - +C
    ignored spec: x /var/tmp/systemd-private-%b-*
    ignored spec: X /var/tmp/systemd-private-%b-*/tmp
    ignored spec: x  /var/lib/systemd/coredump/.#core*.%b*
    ignored spec: z /var/log/journal/%m 2755 root systemd-journal - -
    ignored spec: z /var/log/journal/%m/system.journal 0640 root systemd-journal - -
    <stdin>:37: Failed to resolve user 'uuidd': No such process
    make[1]: *** [fs/ext2/ext2.mk:66: images/rootfs.ext2] Error 65
    make: *** [Makefile:83: _all] Error 2

This error can be reproduced with the commands:

    cat <<EOF >.config
    BR2_aarch64=y
    BR2_TOOLCHAIN_EXTERNAL=y
    BR2_PACKAGE_UTIL_LINUX=y
    BR2_PACKAGE_UTIL_LINUX_UUIDD=y
    BR2_INIT_SYSTEMD=y
    BR2_TARGET_ROOTFS_EXT2=y
    EOF
    make olddefconfig
    make

The error comes from systemctl, which cannot find the uuidd user in
the target rootfs, needed in the uuidd.service unit file [1].

This commit fixes the issue by adding the uuidd user and group in
support/scripts/mkusers syntax.

[1] https://web.git.kernel.org/pub/scm/utils/util-linux/util-linux.git/tree/misc-utils/uuidd.service.in?h=v2.40.2

Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
[Julien: add commands to reproduce the issue in commit log]
Signed-off-by: Julien Olivain <ju.o@free.fr>

package/util-linux/util-linux.mk

@@ -60,6 +60,12 @@ HOST_UTIL_LINUX_CONF_OPTS = \
 	--with-systemdsystemunitdir=no \
 	--without-python
 
+ifeq ($(BR2_PACKAGE_UTIL_LINUX_UUIDD),y)
+define UTIL_LINUX_USERS
+	uuidd -1 uuidd -1 * - - - uuidd user
+endef
+endif
+
 ifneq ($(BR2_PACKAGE_UTIL_LINUX_BINARIES)$(BR2_PACKAGE_UTIL_LINUX_CRAMFS)$(BR2_PACKAGE_UTIL_LINUX_FSCK)$(BR2_PACKAGE_UTIL_LINUX_LOSETUP),)
 UTIL_LINUX_SELINUX_MODULES = fstools
 endif