Reduce load of bug601 test

The test repeatedly creates connections which exhausts all the available
TCP connections. The test doesn't appear to test any specific
functionality with the repeated reconnections which means removing it
shouldn't be a problem.

maxscale-system-test/bug601.cpp

@@ -132,15 +132,17 @@ int main(int argc, char* argv[])
 
 void* parall_traffic(void* ptr)
 {
-    MYSQL* conn;
     while (exit_flag == 0)
     {
-        conn = Test->maxscales->open_rwsplit_connection(0);
-        mysql_close(conn);
-        if (Test->backend_ssl)
+        MYSQL* conn = Test->maxscales->open_rwsplit_connection(0);
+
+       while (exit_flag == 0 && mysql_query(conn, "DO 1") == 0)
         {
             sleep(1);
         }
+
+        mysql_close(conn);
     }
+
     return NULL;
 }