Make routers_client 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 routers_client use **kwargs.

Partially implements blueprint consistent-service-method-names

Change-Id: I2db862191cc30bcf903098d2959b9b22b16c153b
diff --git a/tempest/common/dynamic_creds.py b/tempest/common/dynamic_creds.py
index 2ffc92d..5f6c8b8 100644
--- a/tempest/common/dynamic_creds.py
+++ b/tempest/common/dynamic_creds.py
@@ -240,7 +240,7 @@
         external_net_id = dict(
             network_id=CONF.network.public_network_id)
         resp_body = self.routers_admin_client.create_router(
-            router_name,
+            name=router_name,
             external_gateway_info=external_net_id,
             tenant_id=tenant_id)
         return resp_body['router']