MDEV-8211 plugins.server_audit fails sporadically in buildbot.

Connection event can happen before the query ends. Added a delay to
   confirm the order.

mysql-test/suite/plugins/t/server_audit.test

@@ -13,6 +13,7 @@ set global server_audit_incl_users=null;
 set global server_audit_file_path='server_audit.log';
 set global server_audit_output_type=file;
 set global server_audit_logging=on;
+--sleep 2
 connect (con1,localhost,root,,mysql);
 connection default;
 disconnect con1;