San Mateo-based Coupa Software Inc. said Tuesday that it will pay about $215 million in cash to acquire Exari Group, Inc., a Boston-based company that makes contract lifecycle management software. Coupa makes business expense management software company and said Exari's capabilities will complement its existing platform. In an interview with the Business Journal late last year, Coupa CEO and Chairman Rob Bernshteyn explained his company's business model: "I felt that this was one of the big areas...