Run the script and add it to the list of threads.

def push_script(self, scriptable, script, callback=None):
        """Run the script and add it to the list of threads."""
        if script in self.threads:
            self.threads[script].finish()
        thread = Thread(self.run_script(scriptable, script),
                                      scriptable, callback)
        self.new_threads[script] = thread
        return thread