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

unstack.sh

@@ -111,5 +111,5 @@ fi
 # Quantum dhcp agent runs dnsmasq
 if is_service_enabled q-dhcp; then
     pid=$(ps aux | awk '/[d]nsmasq.+interface=tap/ { print $2 }')
-    [ ! -z $pid ] && sudo kill -9 $pid
+    [ ! -z "$pid" ] && sudo kill -9 $pid
 fi