host-deploy: ovirt-node: do not activate bridge plugin in non-legacy nodes

ovirt-node will be provided with or without the bridge per interface, in
case we do not have these bridges we can allow the engine post installation
to setup the networking.

Change-Id: I1ecbec6c34a8a38518c0c36d1674c5fe820aac2b
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>