deflogin: explicit ROOTPW_EMPTY

This relates to commit f2892ad3e4f281e83b0ec7c4131ff248b1ff4bd7
as there's an obvious need to be able to set empty root password
for LiveCDs but previous implementation was very fragile (and is
going to stay that way) -- so clear and separate knob for making
an image defenseless looks better.
deflogin: refactoring and fixup

There have been several problems with this feature:
- a typo;
- non-existant GROUPS (even a single one) would block setting
  all of the supplementary groups but separately-set 'wheel';
- this feature isn't used much actually so sees no battle testing.

The typo has been just fixed; GROUPS are now applied by iteration
which is less effective but more reliable; an additional script
hook to write down login invitation for the first passwordless
account (if any) has been implemented; and several more group
managing targets have been added (based on live feature's script).
live: use/deflogin (along with fixups)

It appears that live feature has been buggy regarding user
groups: its 30-users script would create a predefined account
with fixed supplementry groups list, and even if deflogin feature
got used too it would fail to add any groups to already existing
account since its useradd(8) call would fail.

Let's drop this duplication which has been long overdue anyways.

Thanks dd@ for both reporting the problem and carrying out
initial investigation.
Revert "regular.mk: use imagewriter"

This reverts commit fd8f375573951280d1ae06f2d7dd559fab9caef9.
xdg-su is broken (some would say beyond repair) regarding DE
detection and handling of various GUI helper utilities,
especially in graceful fallback department; only a few images
can get imagewriter until this is fixed, let kde4 be the one.
server.mk: shift use/power/acpi/button to server-mini

It used to be added in server-ovz but it really belongs to
the underlying server-mini already as more images built
upon that one should perform correct shutdown given ATX
compatible case/mobo or a VM that can do ACPI.
server: added zabbix target

This is a refactored result of Zabbix-related experiments;
we can do a rough zabbix server sketch that still requires
its own setup to go.

NB: both the pkglist and the target are describing several
distinct things actually: zabbix server, zabbix agent,
and the underlying SQL/HTTP/SMTP servers which might get
their own smaller targets some day.
server.mk, test.mk: added zabbix images

server-zabbix.iso is ready for deployment,
and live-zabbix.iso is zabbix agent + firefox
(needs at least Server to be specified properly
within zabbix_agentd.conf when booted).
live.mk: minor live-gimp updates

cvltonemap is no more available in sisyphus/p7;
xsane and usbutils were sorely missing (thanks dd@).

NB: fim is currently i586-only, need to fix or drop it.
syslinux: add forensics mode

A variant of rescue that marks the need to be careful
towards block devices and filesystems thus reducing
the amount of auto-activation done by startup-rescue
(0.17 or newer).
rescue+misc: added lsof

Wonder how it's been missing for 3+ years...
regular.mk: added forensics mode to rescue flavour

Just a convenient knob for a few things done previously
to help spare the interesting bits from being overrun.

NB: live_rw isn't added although it might be useful
    since that would yield too many boot targets overall;
    this is likely to change some day, hopefully when
    media type detection/handling is implemented.

Let's bump syslinux timeout to 20 seconds either
so that iKVM users have a chance to select anything
and not just see the default booting after a few
screen area size changes.
1.1.31-alt1

- live: refactoring
- forensics mode
gear-store-tags