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/lib/nova b/lib/nova
index 333695e..dbfc294 100644
--- a/lib/nova
+++ b/lib/nova
@@ -213,7 +213,7 @@
             fi
         fi
 
-        if is_service_enabled quantum && [[ $Q_PLUGIN = "openvswitch" ]] && ! sudo grep -q '^cgroup_device_acl' $QEMU_CONF ; then
+        if is_service_enabled quantum && is_quantum_ovs_base_plugin "$Q_PLUGIN" && ! sudo grep -q '^cgroup_device_acl' $QEMU_CONF ; then
             # Add /dev/net/tun to cgroup_device_acls, needed for type=ethernet interfaces
             cat <<EOF | sudo tee -a $QEMU_CONF
 cgroup_device_acl = [