By LAURENCE ILIFF MEXICO CITY — When Barack Obama visits Mexico City in a few weeks, he will probably stay in the presidential suite at one of the big chain hotels such as the Four Seasons or the Sheraton (next to the U.S. Embassy), or in one of the towers in the upscale Polanco area.But in the hip Condesa neighborhood on a side street surrounded by parks, Obama already has a room with his name on it in a luxury boutique hotel.