Split out Neutron subnets client

Splitting out a subnets client for Neutron.

Partially implements blueprint consistent-service-method-names

Change-Id: I52c9d099b97540440fa98343c736b894d130a07e
diff --git a/tempest/tests/cmd/test_javelin.py b/tempest/tests/cmd/test_javelin.py
index 4a8f729..fc3d984 100644
--- a/tempest/tests/cmd/test_javelin.py
+++ b/tempest/tests/cmd/test_javelin.py
@@ -380,7 +380,7 @@
 
         javelin.destroy_subnets([self.fake_object])
 
-        mocked_function = self.fake_client.networks.delete_subnet
+        mocked_function = self.fake_client.subnets.delete_subnet
         mocked_function.assert_called_once_with(fake_subnet_id)
 
     def test_destroy_routers(self):