Zabbix

.......... [DEV-2405] refactored libzbxdbupgrade

Merge in ZBX/zabbix from feature/DEV-2405-6.5 to master

* commit 'f2698ebaa1845aa16245f89f95ab56c1d4b56b11':
  .......... [DEV-2405] fixed naming
  .......... [DEV-2405] fixed warnings
  .......... [DEV-2405] remove empty line
  .......... [DEV-2405] code review rework
  .......... [DEV-2405] refactored libzbxdbupgrade