WASHINGTON (Reuters) - U.S. President Barack Obama will travel to Poland and Spain next month to attend the NATO Summit, including a bilateral meeting with Polish President Andrzej Duda to discuss security issues, the White House said on Monday.  Obama will attend his last NATO summit in Warsaw from July 7 to July 9, the White House said in a statement. He then travels to meet with leaders in Spain, a NATO ally, from July 9 to July 11, it said. 