Make add_router_to_l3_agent use **kwargs

As we discussed on
http://lists.openstack.org/pipermail/openstack-dev/2015-July/068864.html
All http POST/PUT methods need to contain **kwargs as their arguments.

This patch makes add_router_to_l3_agent of network client
to use **kwargs.

Partially implements blueprint consistent-service-method-names

Change-Id: I2f17062076a3a356bbb2f67099bcc9b3edd2f76f
diff --git a/tempest/scenario/test_network_basic_ops.py b/tempest/scenario/test_network_basic_ops.py
index 28f1cd3..2f0b406 100644
--- a/tempest/scenario/test_network_basic_ops.py
+++ b/tempest/scenario/test_network_basic_ops.py
@@ -726,7 +726,7 @@
         target_agent = list(hosting_agents if no_migration else
                             agent_list - hosting_agents)[0]
         schedule_router(target_agent,
-                        self.router['id'])
+                        router_id=self.router['id'])
         self.assertEqual(
             target_agent,
             list_hosts(self.router.id)['agents'][0]['id'],