Ctor 264 plugin database mysql mode databasesize change the way we calculate the fragmentation rate

[omercier]

Description

REFS: CTOR-264

Enhanced the way the fragmentation is calculated.

Fixes #4761

Type of change

• Patch fixing an issue (non-breaking change)
• New functionality (non-breaking change)
• Functionality enhancement or optimization (non-breaking change)
• Breaking change (patch or feature) that might cause side effects breaking part of the Software

How this pull request can be tested ?

On a Centreon server:

/usr/lib/centreon/plugins//centreon_mysql.pl --plugin=database::mysql::plugin  --host=127.0.0.1 --username='centreon' --password='centreon' --port=''  --mode=databases-size --filter-database='^(?!(information_schema|performance_schema|test))' --filter-perfdata='database' --verbose --warning-table-frag=1

Checklist

• I have followed the coding style guidelines provided by Centreon
• I have commented my code, especially hard-to-understand areas of the PR.
• I have rebased my development branch on the base branch (develop).
• I have implemented automated tests related to my commits.
• I have reviewed all the help messages in all the .pm files I have modified.
  • All sentences begin with a capital letter.
  • All sentences are terminated by a period.
  • I am able to understand all the help messages, if not, exchange with the PO or TW to rewrite them.