Zabbix

........S. [ZBXNEXT-3480] use an array of strings in the inventory structure

The ZBX_DC_HOST_INVENTORY structure now use an array of
strings for storing the various inventory fields.
This is necessary because, in the previous commit, the problem
of synchronizing the configuration cache on the fly was not
fully considered.
Now this diff prepare the ground for indexing the fields that need
to be updated in the configuration cache in an easy way.

Discussed with Andris Zeila.