MIAMI (Reuters) - Two teenage car thieves drove a stolen car on Wednesday without being stopped onto the U.S. military base that commands much of the war on terror, triggering an investigation into the security breach, police and military officials said. Police in Tampa, Florida, said the joyriders were only stopped and arrested after ramming two police cruisers that had entered MacDill Air Force Base in pursuit. Police had been monitoring the vehicle as it sped through the Florida Gulf Coast city after eluding a police speed trap, said police spokeswoman Laura McElroy. The car then "blasted through the gate...