fix(rrd): broker config generate external values

[sc979]

Pull Request Template

Description

Broker configuration doesn't generate rrdcached external information in a new install.

Type of change

• Patch fixing an issue (non-breaking change)
• New functionality (non-breaking change)
• Breaking change (patch or feature) that might cause side effects breaking part of the Software
• Updating documentation (missing information, typo...)

Target serie

• 18.10.x
• 19.04.x (master)

How this pull request can be tested ?

Install a new centreon. (Or delete rrdcached external information: delete from cfg_centreonbroker_info where config_key IN ('path', 'port') AND config_group_id = 0 AND config_group = 'output')

Add rrdcached configuration in 'Administration > Paramaters > rrdtool' and generate configuration for the central server:

• before the patch: you don't have rrdcached information in /etc/centreon-broker/central-rrd.xml file
• after the patch: you have rrdcached information in /etc/centreon-broker/central-rrd.xml file

Checklist

Community contributors & Centreon team

• I followed the coding style guidelines provided by Centreon
• I have commented my code, especially new classes, functions or any legacy code modified. (docblock)
• I have commented my code, especially hard-to-understand areas of the PR.
• I have made corresponding changes to the documentation.
•  I have rebased my development branch on the base branch (master, maintenance).

Centreon team only

• I have made sure that the unit tests related to the story are successful.
• I have made sure that unit tests covers 80% of the code written for the story.
• I have made sure that acceptance tests related to the story are successful (local and CI)

[sc979]

PR from @garnier-quentin, already reviewed by kduret and myself (7396)