Fix broken test on Python 3

tests/service_test.py

@@ -185,13 +185,13 @@ class ServiceTest(DockerClientTestCase):
     def test_start_container_creates_ports(self):
         service = self.create_service('web', ports=[8000])
         container = service.start_container().inspect()
-        self.assertEqual(container['HostConfig']['PortBindings'].keys(), ['8000/tcp'])
+        self.assertEqual(list(container['HostConfig']['PortBindings'].keys()), ['8000/tcp'])
         self.assertNotEqual(container['HostConfig']['PortBindings']['8000/tcp'][0]['HostPort'], '8000')
 
     def test_start_container_creates_port_with_explicit_protocol(self):
         service = self.create_service('web', ports=['8000/udp'])
         container = service.start_container().inspect()
-        self.assertEqual(container['HostConfig']['PortBindings'].keys(), ['8000/udp'])
+        self.assertEqual(list(container['HostConfig']['PortBindings'].keys()), ['8000/udp'])
 
     def test_start_container_creates_fixed_external_ports(self):
         service = self.create_service('web', ports=['8000:8000'])