fixed random error with networks in unit tests

Change-Id: I8f6eb850d688b676389991d0400fddc6bef4e31b

nailgun/nailgun/api/models.py

@@ -187,8 +187,12 @@ class Cluster(Base):
     # During cluster deletion sqlalchemy engine will set null
     # into cluster foreign key column of notification entity
     notifications = relationship("Notification", backref="cluster")
-    network_groups = relationship("NetworkGroup", backref="cluster",
-                                  cascade="delete")
+    network_groups = relationship(
+        "NetworkGroup",
+        backref="cluster",
+        cascade="delete",
+        order_by="NetworkGroup.id"
+    )
     replaced_deployment_info = Column(JSON, default={})
     replaced_provisioning_info = Column(JSON, default={})
     is_customized = Column(Boolean, default=False)

nailgun/nailgun/test/integration/test_cluster_collection_handlers.py

@@ -36,7 +36,7 @@ class TestHandlers(BaseIntegrationTest):
                     {"cluster_id": cluster_id}),
             headers=self.default_headers,
         ).body)["networks"]
-        return sorted(nets, key=lambda n: n['vlan_start'])
+        return nets
 
     def test_cluster_list_empty(self):
         resp = self.app.get(