replace dict.iteritems() with six.iteritems(dict)

According to https://wiki.openstack.org/wiki/Python3 dict.iteritems()
should be replaced with six.iteritems(dict).

Change-Id: Ia2dcabbd071e1fcdf111ba83573785989a77aef0
Merge "replace dict.iteritems() with six.iteritems(dict)"