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>
Merge "Quantum/plugins/ryu: minor update for Quantum Ryu plugin"