add killing mysqld process after snapshot revert

maxscale-system-test/mariadb_nodes.cpp

@@ -916,6 +916,7 @@ bool Mariadb_nodes::revert_nodes_snapshot()
         {
             rval = false;
         }
+        ssh_node_f(i, true, "pkill -9 mysqld");
     }
     return rval;
 }