Bug 1597975 - Fix manifestparser in python 3 r=ahal

This patch fixes a minor issue with manifestparser when it is used in python 3. The problem was that dict.items() returns a generator in python 3 instead of a list.

Differential Revision: https://phabricator.services.mozilla.com/D53953

--HG--
extra : moz-landing-system : lando

testing/mozbase/manifestparser/manifestparser/manifestparser.py

@@ -196,7 +196,7 @@ class ManifestParser(object):
 
             # otherwise an item
             # apply ancestor defaults, while maintaining current file priority
-            data = dict(self._ancestor_defaults.items() + data.items())
+            data = dict(list(self._ancestor_defaults.items()) + list(data.items()))
 
             test = data
             test['name'] = section