Val Chmerkovskiy and Jenna Johnson are about to mambo into marriage.  The fellow Dancing With the Stars ballroom pros got engaged in Venice on Thursday after the future groom got down on one knee in a Venetian square. Johnson was shocked as her longtime beau presented her with a stunning sparkler during their trip. Of course, she said yes and planted a kiss on her soon-to-be husband.  "I can't wait to make you my wife," he later wrote to her on Instagram while announcing the engagement news.  The star wasn't kidding. As Susan of Jacob & Co. told E! News, the dancer was very involved in the process of purchasing a ring for his new fiancée. The...