Blackstone Group LP has agreed to buy a controlling stake in Essel Propack Ltd., as the parent of the Indian packaging supplier to Colgate-Palmolive Co. and Olay Co. sells assets to pay debt. The world’s largest alternative asset manager will acquire 51 percent of Essel Propack for $310 million from one of the founders, Ashok Goel Trust, Essel Propack said in a statement on Monday. The move will trigger an open offer to buy an additional 26 percent of the shares, according to the statement.