Python 3: use six.iteritems() instead of iteritems()

Six.iteritems() replaces dictionary.iteritems() on Python 2 and
dictionary.items() on Python 3.

Change-Id: I12fda5f20d2f4fe8227e45b2fe46b332f63deb97
Merge "Python 3: use six.iteritems() instead of iteritems()"