I've hit this same issue with all my libvirt-managed kvm VMs too:
$ virsh start sec-hardy-i386 error: Failed to start domain sec-hardy-i386 error: Failed to add tap interface to bridge 'br0': No such file or directory
I've hit this same issue with all my libvirt-managed kvm VMs too:
$ virsh start sec-hardy-i386
error: Failed to start domain sec-hardy-i386
error: Failed to add tap interface to bridge 'br0': No such file or directory