Zabbix

...G...PS. [ZBXNEXT-1862] modified server, proxy and agent to follow changes in /etc/resolv.conf

Before this change:
   - server, proxy and agent read /etc/resolv.conf file only on startup. Later, when /etc/resolv.conf was updated
     (e.g. DNS servers changed) the old content of /etc/resolv.conf was in effect, Zabbix had to be restarted
     to pick up changes. One exception is Debian GNU/Linux, which reacts to /etc/resolv.conf update without
     Zabbix modification.
After this change:
   - server, proxy and agent check modification time of /etc/resolv.conf regularly in main loop and reinitialize
     resolver when the modification time changes.