system VM looking for cloud0 bridge when OVS/GRE isolation is enabled

[Kuang-Ching Wang]

Hi, I am trying to set up my cloudstack using OVS plugin.  I created an 
advanced zone with GRE isolation.  When enabling zone, system VMs cannot start 
with the following exception.  What did I miss?

2014-06-30 21:46:38,382 WARN  [kvm.resource.LibvirtComputingResource] 
(agentRequest-Handler-3:null) LibvirtException
org.libvirt.LibvirtException: Cannot get interface MTU on 'cloud0': No such 
device
        at org.libvirt.ErrorHandler.processError(Unknown Source)
        at org.libvirt.Connect.processError(Unknown Source)
        at org.libvirt.Connect.processError(Unknown Source)
        at org.libvirt.Connect.domainCreateXML(Unknown Source)
        at 
com.cloud.hypervisor.kvm.resource.LibvirtComputingResource.startVM(LibvirtComputingResource.java:1213)
        at 
com.cloud.hypervisor.kvm.resource.LibvirtComputingResource.execute(LibvirtComputingResource.java:3659)
        at 
com.cloud.hypervisor.kvm.resource.LibvirtComputingResource.executeRequest(LibvirtComputingResource.java:1307)
        at com.cloud.agent.Agent.processRequest(Agent.java:498)
        at com.cloud.agent.Agent$AgentRequestHandler.doTask(Agent.java:806)
        at com.cloud.utils.nio.Task.run(Task.java:83)
        at 
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1146)
        at 
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
        at java.lang.Thread.run(Thread.java:701)