'Make an image node by safely calling Image.run (i.e. ensure the file exists).'

def _make_image_node(self):

    self.arguments.append(os.path.join('/', SS_DUMP_DIR, (self.filename + '.png')))
    screenshot_file = (os.path.join(OUTPUT_PATH, self.filename) + '.png')
    if (not os.path.isfile(screenshot_file)):
        open(screenshot_file, 'w').close()
    (image_node,) = Image.run(self)
    return image_node
