The Roomba from Bedford’s iRobot Crop. is already an Internet sensation, starring in YouTube videos of babies and kittens ridding the self-propelled vacuum cleaners. So to create its ad campaign, which begins Tuesday in North America, the company looked to the Web, using music from a YouTube song about the Roomba and hiring a robot dancer whose online video has 43 million views. The $10 million campaign is part of the company’s effort to boost consumer sales as its military business is expected to decline.