replace dict.iteritems() with six.iteritems(dict)
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: If7c7a286af559559060037aa80aea65b21c5c4ee

varunarya10/python-ironicclient,openstack/python-ironicclient,bcrochet/python-ironicclient,rdo-management/python-ironicclient,openstack/python-ironicclient,ramineni/myclient,redhat-openstack/python-ironicclient,CiscoUcs/UCS-python-ironicclinet,JioCloud/python-ironicclient,NaohiroTamura/python-ironicclient,NaohiroTamura/python-ironicclient