CRAWFORD, Texas (Reuters) - President George W. Bush, an avid mountain biker, got a chance to test his mettle against cycling superstar Lance Armstrong on Saturday. The seven-time Tour de France champion joined the president for a two-hour, 17-mile trek through the canyons and river-crossings of Bush's 1,600-acre Texas ranch. Armstrong, a fellow Texan and Bush friend who nonetheless disagrees with the president on the Iraq war, called it a "dream scenario" to cycle with the president. While many Americans wonder what attracts Bush to the Prairie Chapel ranch, where is he spending the month of August, Armstrong said he...