Set Default Hostname to use the defaults rather than set to Zabbix Server

Hey gplessis
this is a pull request that adds a patch to the default zabbix_agentd.conf file, basically it disables the Hostname item (comments out) so that zabbix will be forced to use the default HostnameItem to populate the agent hostname value - which by default uses the system hostname configured.

this should help for faster roll outs as end users only have to edit the 2 server fields to get going initially

ultimately that could be configured as a install config step (much like you have to set mysql root password the first time its installed)