zabbix: correct pidfile und update initscript

zabbix: correct pidfile und update initscript

zabbix_agentd will not start because the initscript checks an old
path to the configfile and then zabbix_agentd uses the new path.
(old /etc/zabbix/zabbix_agentd.conf   new /etc/zabbix_agentd.conf)
I think the new path is better as most people have only one zabbix
tool installed on their embedded device.

Further there is a problem with the pid-file: zabbix creates it by
default in /tmp, and the init script creates a folder in
/var/run/zabbix where the pid-file is expected. start-stop-daemon will
not find the pid-file and cannot stop zabbix_agentd. So I changed the
initscript and conffile to use the same pid-file. I actually chose
/var/run/zabbix_agentd.conf instead of creating a subfolder or use /tmp.

While doing that I redid the whole initscript and changed additionally:
- move conffile to new location if is in the location from before
  changeset #32497
- only create zabbix users if there is no AllowRoot=1 in config
- only support the pid-file path /var/run/zabbix_agentd.pid, check it
  in initscript and warn if it is changed.
- don't log to a file in /tmp, but use syslog
- only start one passive check agent instead of default 3
- don't search actively for a zabbix-server on 127.0.0.1
- don't set the hostname to "Zabbix server" but use system.hostname

Signed-off-by: Stefan Hellermann <stefan@the2masters.de>
Signed-off-by: Florian Fainelli <florian@openwrt.org>
git-svn-id: svn://svn.openwrt.org/openwrt/packages@34492 3c298f89-4303-0410-b956-a3cf2f4a3e73