Switch all uses of iteritems to use six instead

This commit switches all of the uses of iteritems in tempest to use
six.iteritems() instead so it can be run using python2 or python3.

Change-Id: Ice006bc5238edb072a9556559b467804d4604d49
diff --git a/tempest/api/network/test_dhcp_ipv6.py b/tempest/api/network/test_dhcp_ipv6.py
index 8be0100..ca08fbd 100644
--- a/tempest/api/network/test_dhcp_ipv6.py
+++ b/tempest/api/network/test_dhcp_ipv6.py
@@ -16,6 +16,7 @@
 import netaddr
 import random
 
+import six
 from tempest_lib.common.utils import data_utils
 from tempest_lib import exceptions as lib_exc
 
@@ -127,7 +128,7 @@
         ):
             kwargs = {'ipv6_ra_mode': ra_mode,
                       'ipv6_address_mode': add_mode}
-            kwargs = {k: v for k, v in kwargs.iteritems() if v}
+            kwargs = {k: v for k, v in six.iteritems(kwargs) if v}
             real_ip, eui_ip = self._get_ips_from_subnet(**kwargs)
             self._clean_network()
             self.assertEqual(eui_ip, real_ip,
@@ -284,7 +285,7 @@
         ):
             kwargs = {'ipv6_ra_mode': ra_mode,
                       'ipv6_address_mode': add_mode}
-            kwargs = {k: v for k, v in kwargs.iteritems() if v}
+            kwargs = {k: v for k, v in six.iteritems(kwargs) if v}
             subnet = self.create_subnet(self.network, **kwargs)
             port = self.create_port(self.network)
             port_ip = next(iter(port['fixed_ips']), None)['ip_address']
@@ -311,7 +312,7 @@
         ):
             kwargs = {'ipv6_ra_mode': ra_mode,
                       'ipv6_address_mode': add_mode}
-            kwargs = {k: v for k, v in kwargs.iteritems() if v}
+            kwargs = {k: v for k, v in six.iteritems(kwargs) if v}
             subnet = self.create_subnet(self.network, **kwargs)
             ip_range = netaddr.IPRange(subnet["allocation_pools"][0]["start"],
                                        subnet["allocation_pools"][0]["end"])
@@ -389,7 +390,7 @@
         ):
             kwargs = {'ipv6_ra_mode': ra_mode,
                       'ipv6_address_mode': add_mode}
-            kwargs = {k: v for k, v in kwargs.iteritems() if v}
+            kwargs = {k: v for k, v in six.iteritems(kwargs) if v}
             subnet, port = self._create_subnet_router(kwargs)
             port_ip = next(iter(port['fixed_ips']), None)['ip_address']
             self._clean_network()