extract read_config_files util for config parsing

plugins/builder/save_failed_tree.py

@@ -3,7 +3,6 @@ import fnmatch
 import os
 import sys
 import tarfile
-import six.moves.configparser
 
 import koji
 import koji.tasks as tasks
@@ -28,8 +27,7 @@ def omit_paths3(tarinfo):
 
 def read_config():
     global config
-    cp = six.moves.configparser.SafeConfigParser()
-    cp.read(CONFIG_FILE)
+    cp = koji.read_config_files(CONFIG_FILE)
     config = {
         'path_filters': [],
         'volume': None,