we only want one handler for shell output

so that multiple calls of the set_up_logging function do not create multiple
handlers (and then undesired multiple outputs for one plog message)

src/mpsd_software_manager/mpsd_software.py

@@ -339,10 +339,11 @@ def set_up_logging(loglevel="warning", file_path=None):
     # create formatter 'empty' formatter
     formatter = logging.Formatter("%(message)s")
 
-    # create, format and add handler for shell output
+    # create, format and set handler for shell output
     ch = logging.StreamHandler()
     ch.setFormatter(formatter)
-    print_log.addHandler(ch)
+    print_log.handlers = [ch]
+
 
     # if filename provided, write output of print_log to that file, too
     if file_path: