Fix python3 support in yaml-validate script.

Python3 drops the "iteritems" method for dict in favor to
"items".

Change-Id: I8d21233e917b5d36be385d59f1a7c9a0588aea2d
Closes-Bug: 1783988

tools/yaml-validate.py

@@ -810,7 +810,7 @@ def _rsearch_keys(d, pattern, search_keynames=False, enter_lists=False):
             path = []
         # recursively walk through the dict, optionally entering lists
         if isinstance(d, dict):
-            for k, v in d.iteritems():
+            for k, v in d.items():
                 path.append(k)
                 if (isinstance(v, dict) or enter_lists and
                     isinstance(v, list)):

tox.ini

@@ -16,6 +16,7 @@ commands = python setup.py testr --slowest --testr-args='{posargs}'
 commands = {posargs}
 
 [testenv:pep8]
+basepython = python3
 whitelist_externals =
     bash
 commands =