Quantum/plugins/ryu: minor update for Quantum Ryu plugin

- updated package list for Ryu
  ryu plugin/agent needs python-netifaces
- quantum-ryu-agent also needs ryu module

Change-Id: I5b49efceb65e8139a49a8e82f55ea6aa7d1eebac
Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
diff --git a/files/apts/ryu b/files/apts/ryu
index 1e8f2d2..4a4fc52 100644
--- a/files/apts/ryu
+++ b/files/apts/ryu
@@ -1,4 +1,5 @@
 python-setuptools
 python-gevent
 python-gflags
+python-netifaces
 python-sphinx