Fix bug solettaproject#1516:

    update logging instantiation codes to solve issue when invoke the tools/run-fbp-tests with --log option
    refer to: https://docs.python.org/2/library/logging.html#module-level-functions

tools/run-fbp-tests

@@ -321,11 +321,7 @@ def set_log_level(args):
         if not level:
             raise ValueError('Invalid log level: %s' % args.log)
 
-    root = logging.getLogger()
-    hdlr = root.handlers[0]
-    fmt = logging.Formatter('%(message)s')
-    hdlr.setFormatter(fmt)
-    hdlr.setLevel(level)
+    logging.basicConfig(level=level, format='%(message)s')
 
 if __name__ == "__main__":
     parser = argparse.ArgumentParser()