Add ascent_opts["default_dir"] to "image_name" images (#1295)

image_name will respect default_dir unless provided a path.

src/libs/ascent/runtimes/flow_filters/ascent_runtime_rendering_filters.cpp

@@ -1352,6 +1352,7 @@ DefaultRender::execute()
       if(params().has_path("image_name"))
       {
         image_name =  params()["image_name"].as_string();
+        image_name = output_dir(image_name);
       }
       else
       {