Atlanta Is A Magnet For Upwardly Mobile Blacks By Patricia J. Mays AP ATLANTA - Four months ago, Ronnie Harris quit his job as a safety engineer for the city of San Antonio, sold all his furniture, leased his four-bedroom ranch house and moved to Atlanta. Harris, 36 and divorced, didn't have a job or a place to live but was intent on settling in a place with a booming economy and a growing community of young, upwardly mobile blacks. For many like Harris, there is only one place to move. "I chose Atlanta because it's the place to be," he said. "It's the black mecca." Within weeks of his arrival, Harris landed a job as an insurance adjuster and found many other like-minded transplants lured here by a rich mix of job opportunities, black culture and civil-rights legacy. "The climate is good, the cost of living still isn't as bad as New York or L.A., it has a nightlife," said Raymond Winbush, director of the Race Relation