Julia Hart’s new film “Don’t Say Good Luck” opens with Elizabeth (Melanie Lynskey) being mother of the year, before hinting at her inevitable doom. Melanie Lynskey isn’t the star of “Don’t Say Good Luck,” but she is the glue that holds it together. “Don’t Say Good Luck” feels honest. But again, more than anything, “Don’t Say Good Luck” revolves around Lynskey. Everything in “Don’t Say Good Luck” revolves around her and the delicate, believable choices she makes.