Add support for the Quantum Ryu plugin.

This patch allows using the Quantum Ryu plugin.
Ryu plugin lets Quantum link Open vSwitch and Ryu OpenFlow controller[1].

Ryu OpenFlow controller is not Openstack component, but I added some
processing that is related with Ryu to stack.sh for the convenience of
the person who intend to try the plugin.

Instructions for using Ryu plugin:
1. Enable services: "q-svc", "q-agt", "q-dhcp", "q-l3", "quantum", "ryu"
2. Set Q_PLUGIN to "ryu"
3. Set an internal network interface name to connect br-int on plural
   hosts to RYU_INTERNAL_INTERFACE (optional)

Example localrc:
  disable_service n-net
  enable_service q-svc q-agt q-dhcp q-l3 quantum ryu
  Q_PLUGIN=ryu
  RYU_INTERNAL_INTERFACE=eth1

[1] http://osrg.github.com/ryu/

Change-Id: Ic1da132fa421f1c70c10a319ee3239831b0f956f
diff --git a/stackrc b/stackrc
index 3002c46..f9a41bd 100644
--- a/stackrc
+++ b/stackrc
@@ -101,6 +101,10 @@
 HEAT_REPO=${GIT_BASE}/heat-api/heat.git
 HEAT_BRANCH=master
 
+# ryu service
+RYU_REPO=https://github.com/osrg/ryu.git
+RYU_BRANCH=master
+
 # Nova hypervisor configuration.  We default to libvirt with **kvm** but will
 # drop back to **qemu** if we are unable to load the kvm module.  ``stack.sh`` can
 # also install an **LXC** or **OpenVZ** based system.