CloudUtils getDevInfo function only checks for KVM bridgePort and not OVS. In case you provide an ovsbridge, getDevInfo(dev) will say it's a device instead of a bridge.
Given a KVM Host with openvswitch networking
and kvmnetworklabel of the guest traffic type specifying the name of an existing OVS bridge.
When cloudstack-setup-agent is run on the host
Then the existing openvswitch bridge is used.
A new bridge cloudbr0 is created in openvswitch.
and the networking scripts define the new bridge as OVS_BRIDGE in the ifcfg of the existing bridge.