* testing/at: Properly set primary group in .pre-install.
testing/at/at.pre-install

* testing/ejabberd: Fix .pre-install script broken since 9716bc3570be.
testing/ejabberd/ejabberd.pre-install

* testing/rrdbot: Remove bogus comment in .pre-install script.
testing/rrdbot/rrdbot.pre-install

* testing/[various]: Add group and use it as primary in .pre-* scripts.
testing/dbmail/dbmail.pre-install
testing/dspam/dspam.pre-install
testing/opensips/opensips.pre-install
testing/pdns/pdns.pre-install
testing/qpage/qpage.pre-install
testing/rrdbot/rrdbot.pre-install
testing/wt/wt.pre-install

Fixes the problem I unintentionally brought in commit ccc056dbf9d3:
system user creation doesn't add same named group and uses nogroup as
primary group unless explicitly specified via -G.

Brings status quo regarding primary groups of users created in packages:
- testing/dbmail
- testing/dspam
- testing/opensips
- testing/pdns
- testing/qpage
- testing/rrdbot
- testing/wt

Now all invocations have following order of arguments (if present):

    addgroup -S -g ... GROUP
    adduser -S -u ... -D -H -h ... -s ... -G ... -g ... USER

Following rules have been applied:
- script starts with shebang !#/bin/sh followed by blank line,
- script ends with exit 0 prepended by blank line,
- only stderr of adduser, addgroup or passwd is redirected to /dev/null,
- getent passwd/group instances has been removed,
- manual checking of file and group existence has been removed,
- `|| true` instances has been removed.

Comments and line wrapping have been preserved.

This way we can avoid ugly default:

    Linux user,,,

Groups and users created by packages shouldn't use high ids by default
(unless explicitly requested), to distinguish them from groups and users
created by administrators for humans.

Following 41 files lacked -S next to addgroup:
- community/sword/sword.pre-install
- main/amavisd-new/amavisd-new.pre-install
- main/chrony/chrony.pre-install
- main/cvechecker/cvechecker.pre-install
- main/dnsmasq/dnsmasq.pre-install
- main/freeradius/freeradius.pre-install
- main/gdnsd/gdnsd.pre-install
- main/haproxy/haproxy.pre-install
- main/haproxy/haproxy.pre-upgrade
- main/kamailio/kamailio.pre-install
- main/logcheck/logcheck.pre-install
- main/mlmmj/mlmmj.pre-install
- main/nrpe/nrpe.pre-install
- main/open-vm-tools/open-vm-tools.pre-install
- main/postgrey/postgrey.pre-install
- main/privoxy/privoxy.pre-install
- main/redis/redis.pre-install
- main/samba/winbind.pre-install
- main/sircbot/sircbot.pre-install
- main/smokeping/smokeping.pre-install
- main/squark/squark.post-install
- main/squid/squid.pre-install
- main/squid/squid.pre-upgrade
- main/subversion/subversion.pre-install
- main/trac/trac.pre-install
- main/vsftpd/vsftpd.pre-install
- main/zabbix/zabbix-agent.pre-install
- testing/3proxy/3proxy.pre-install
- testing/cluster-glue/cluster-glue.pre-install
- testing/elasticsearch/elasticsearch.pre-install
- testing/emby/emby.pre-install
- testing/gdnsd/gdnsd.pre-install
- testing/icinga2/icinga2.pre-install
- testing/lusca/lusca.pre-install
- testing/lusca/lusca.pre-upgrade
- testing/mongodb/mongodb.pre-install
- testing/openxcap/openxcap.pre-install
- testing/prosody/prosody.pre-install
- testing/rancid/rancid.pre-install
- testing/rutorrent/rutorrent.pre-install
- testing/zabbix/zabbix-agent.pre-install

Following 60 files lacked -S next to adduser:
- community/caddy/caddy.pre-install
- community/domoticz/domoticz.pre-install
- community/minetest/minetest-server.pre-install
- community/oscam/oscam.pre-install
- community/seafile/seafile-server.pre-install
- community/syncthing/syncthing.pre-install
- main/apache2/apache2.pre-install
- main/aports-build/aports-build.pre-install
- main/atheme-iris/atheme-iris.pre-install
- main/bind/bind.pre-install
- main/clamav/clamav-db.pre-install
- main/clamsmtp/clamsmtp.pre-install
- main/clamsmtp/clamsmtp.pre-upgrade
- main/coova-chilli/coova-chilli.pre-install
- main/cvechecker/cvechecker.pre-install
- main/dhcp/dhcp.pre-install
- main/distcc/distcc.pre-install
- main/djbdns/dnscache.pre-install
- main/djbdns/tinydns.pre-install
- main/dovecot/dovecot.pre-install
- main/ez-ipupdate/ez-ipupdate.pre-install
- main/fetchmail/fetchmail.pre-install
- main/freeswitch/freeswitch.pre-install
- main/gitolite/gitolite.pre-install
- main/gnats/gnats.pre-install
- main/gross/gross.pre-install
- main/icecast/icecast.pre-install
- main/kamailio/kamailio.pre-install
- main/lighttpd/lighttpd.pre-install
- main/mariadb/mariadb.pre-install
- main/memcached/memcached.pre-install
- main/ngircd/ngircd.pre-install
- main/nrpe/nrpe.pre-install
- main/openntpd/openntpd.pre-install
- main/postgrey/postgrey.pre-install
- main/snort/snort.pre-install
- main/squid/squid.pre-install
- main/squid/squid.pre-upgrade
- main/subversion/subversion.pre-install
- main/trac/trac.pre-install
- main/transmission/transmission-daemon.pre-install
- main/ympd/ympd.pre-install
- main/znc/znc.pre-install
- testing/at/at.pre-install
- testing/buildbot-slave/buildbot-slave.pre-install
- testing/buildbot/buildbot.pre-install
- testing/clapf/clapf.pre-install
- testing/cluster-glue/cluster-glue.pre-install
- testing/dbmail/dbmail.pre-install
- testing/dspam/dspam.pre-install
- testing/ejabberd/ejabberd.pre-install
- testing/emby/emby.pre-install
- testing/mongodb/mongodb.pre-install
- testing/opensips/opensips.pre-install
- testing/pdns/pdns.pre-install
- testing/prosody/prosody.pre-install
- testing/qpage/qpage.pre-install
- testing/rrdbot/rrdbot.pre-install
- testing/wt/wt.pre-install
- unmaintained/ejabberd-git/ejabberd-git.pre-install