First there is a rock star, then there is no rock star, then there is: Donovan Leitch, who serenaded the Sixties with such songs as “Wear Your Love Like Heaven,” “Mellow Yellow” and “Season of the Witch,” returns to the spotlight at the 2012 Rock and Roll Hall of Fame – accompanied by John Mellencamp, who introduces Donovan as one of this year’s inductees. Others in this delayed coverage by HBO include… well, for a rundown, and a reaction,