Stop keepalived after the tests

Once the tests are done keepalived must be stopped. This is done to
prevent it from affecting other tests.

maxscale-system-test/keepalived.cpp

@@ -33,6 +33,11 @@ int main(int argc, char* argv[])
         exit(0);
     }
 
+    Test->on_destroy([&](){
+                        Test->maxscales->ssh_node_f(0, true, "service keepalived stop");
+                        Test->maxscales->ssh_node_f(1, true, "service keepalived stop");
+                    });
+
 
     Test->check_maxscale_alive(0);
     Test->check_maxscale_alive(1);