Fix unit test for ryu-agent

Fixes bug #1197670

This patch fixes programming error in the unit test for ryu-agent.
- Change the way of patch to cfg of ryu-agent
- Fix typo
 s/assert_calls/assert_has_calls/

Change-Id: I9a5a17f314eb9c786338463e077cadc32d846dba
Merge "Fix unit test for ryu-agent"