Tune galera multithreading options to match VM resources

In the integration tests on virtual environments, database
nodes have only 2 vCPU.
Set the parameters to configure mysql/galera to use
less CPU than defaults, using the patch [1]

Related-Bug: https://mirantis.jira.com/browse/PROD-16528

[1] https://gerrit.mcp.mirantis.net/#/c/16627/

Change-Id: I39e542da95496b36080ccfe4be9b399405f40c3d
9 files changed