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
diff --git a/classes/cluster/virtual-mcp-pike-ovs/openstack/init.yml b/classes/cluster/virtual-mcp-pike-ovs/openstack/init.yml
index 77cf4da..3325580 100644
--- a/classes/cluster/virtual-mcp-pike-ovs/openstack/init.yml
+++ b/classes/cluster/virtual-mcp-pike-ovs/openstack/init.yml
@@ -21,6 +21,11 @@
     galera_server_cluster_name: openstack_cluster
     galera_server_maintenance_password: workshop
     galera_server_admin_password: workshop
+    galera_innodb_read_io_threads: 2
+    galera_innodb_write_io_threads: 2
+    galera_wsrep_slave_threads: 2
+    galera_xtrabackup_parallel: 1
+    galera_error_log_enabled: true
     cluster_vip_address: 172.16.10.254
     cluster_local_address: ${_param:single_address}
     cluster_node01_hostname: ctl01