Fixed python34 comparison issue

Signed-off-by: Zal Daroga <zaldaroga@yahoo.com>

compose/service.py

@@ -560,7 +560,7 @@ class Service(object):
 
     def prioritized_networks(self):
         prioritized_networks = OrderedDict(
-            sorted(self.networks.items(), key=lambda t: t[1].get('priority', 0), reverse=True))
+            sorted(self.networks.items(), key=lambda t: t[1].get('priority', 0) or 0, reverse=True))
         return prioritized_networks
 
     def connect_container_to_networks(self, container):

tests/acceptance/cli_test.py

@@ -1278,7 +1278,8 @@ class CLITestCase(DockerClientTestCase):
         self.base_dir = 'tests/fixtures/networks'
         result = self.dispatch(['-f', 'ordered-networks.yml', 'up', '-d'])
 
-        assert 'Connecting to networks_bar\nConnecting to networks_foo' in result.stdout
+        assert 'Connecting to networks_buzz\nConnecting to networks_foo' \
+               '\nConnecting to networks_bar' in result.stdout
 
     @v3_only()
     def test_up_with_healthcheck(self):

tests/fixtures/networks/ordered-networks.yml

@@ -4,10 +4,12 @@ services:
   web:
     image: busybox
     command: top
-    networks: ["foo", "bar"]
+    networks: ["foo", "bar", "buzz"]
 
 networks:
   foo:
-    priority: 1
+    priority: 2
   bar:
-     priority: 2
+     priority: 1
+  buzz:
+    priority: 3