LibvirtHybridOVSBridgeDriver update for STP
LibvirtHybridOVSBridgeDriver update for STP

Fixes bug 1129055

The patch will set the stp status as 'off' and the bridge
forwarding delay to 0.

Cherry picked from 7aeb17d5bbf20f6ffc1c8ccab71f5cbbb57be9a2

Change-Id: Id6874de0752a23646360590794773e7a7028a945

paulmathews/nova,paulmathews/nova,paulmathews/nova