Remove insecure password warning when using MySQL DB in tests

23:51:43.975 [main] INFO  o.x.t.d.i.j.d.DatabaseContainerExecutor - Setting MySQL permissions to create subwikis
23:51:43.976 [main] DEBUG o.t.c.ExecInContainerPattern - /reverent_pasteur: Running "exec" command: mysql -u root -pxwiki -e grant all privileges on *.* to 'xwiki'@'%' identified by 'xwiki'
23:51:44.929 [main] TRACE o.t.c.ExecInContainerPattern - /reverent_pasteur: stdout: 
23:51:44.930 [main] TRACE o.t.c.ExecInContainerPattern - /reverent_pasteur: stderr: mysql: [Warning] Using a password on the command line interface can be insecure.