Fix some python3 encoding issues

* Add .decode('utf-8') where needed
* Add 'b' to `open` where needed, and remove where unnecessary

Change-Id: I0f03ecf9ed1a78e3b2f15f9469deb9aaab698657
diff --git a/git_config.py b/git_config.py
index a294a0b..f6093a2 100644
--- a/git_config.py
+++ b/git_config.py
@@ -304,8 +304,8 @@
     d = self._do('--null', '--list')
     if d is None:
       return c
-    for line in d.rstrip('\0').split('\0'):  # pylint: disable=W1401
-                                             # Backslash is not anomalous
+    for line in d.decode('utf-8').rstrip('\0').split('\0'):  # pylint: disable=W1401
+                                                             # Backslash is not anomalous
       if '\n' in line:
         key, val = line.split('\n', 1)
       else: