About 1,000 workers in Northern Virginia have a new boss today. Reston-based Maximus Inc. has completed its acquisition of Falls Church-based technology contractor Acentia. It is the latest in a string of acquisitions among mid-tier contractors. Maximus acquired the company for $300 million from private equity firm Snow Phipps Group LLC. The deal adds Acentia's systems modernization, software development, program management and other IT work with federal government and civilian health agencies. Maximus…