LOS ANGELES -- Levi Johnston will make his music video debut as a lover whose romance is thwarted by his girlfriend's disapproving mother, according to a Universal Music Group record label and Johnston's attorney. Johnston, 20, who is Bristol Palin's fiance, has agreed to appear in the video with singer-songwriter Brittani Senser next month in Los Angeles. ... According to a written description of the video's story line, the couple share tender moments before they are driven apart by the young woman's mother. Unaware that her mom's interference forced her boyfriend to go, she "throws herself into her mother's arms....