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
Create a volume from a snapshot from different availability zone.

Version 3 for openStack Folsom release:
- nova/db: Added new 'snapshot_get_host' and 'snapshot_get_all_by_host' API calls.
- nova/volume: Export all snapshot as iSCSI targets at Start of nova-volume
- nova/volume: Export snapshot as iSCSI targets at snapschot create
- nova/volume: Remove snapshot iSCSI target at snapschot delete
- nova/volume: Use iSCSI snapshot target as source for volume creating, filtered by 'iscsi_ip_filter' parameter.
- Do not use iscsi discovery if we know host name.