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
Merge "LibvirtHybridOVSBridgeDriver update for STP" into stable/folsom