Use relative imports for the gdbus/codegen package

But not yet for the config module (but is taken care
of in a followup patch).

https://bugzilla.gnome.org/show_bug.cgi?id=650763

gio/gdbus-2.0/codegen/parser.py

@@ -21,11 +21,11 @@
 #
 # Author: David Zeuthen <davidz@redhat.com>
 
-import dbustypes
-
 import sys
 import xml.parsers.expat
 
+from . import dbustypes
+
 class DBusXMLParser:
     STATE_TOP = 'top'
     STATE_NODE = 'node'