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: I52cc0e89c030d7b6bfc735239638b513410933c5
Merge "replace dict.iteritems() with six.iteritems(dict)"