Change logger name to module itself instead of root

Using root logger will make public module log failed by unknow keyword.
Just change the logger name to module itself could dismiss this impact.
And disable logger.propagate could prevent double outputing.

Change-Id: I18696d124ebac9ca970d502558972e51de759097
Fixes: bug #1105133

bin/swift-bench

@@ -158,7 +158,8 @@ if __name__ == '__main__':
         sys.exit('Termination signal received.')
     signal.signal(signal.SIGTERM, sigterm)
 
-    logger = logging.getLogger()
+    logger = logging.getLogger(__name__)
+    logger.propagate = False
     logger.setLevel({
         'debug': logging.DEBUG,
         'info': logging.INFO,