Add OriginVn support for Evpn routes.

Enhance bgp config parser to allow vn configuration.
Add virtual-network to the schema for enet routes.
Set OriginVn for enet routes received via XMPP.
Check OriginVn while replicating routes to enet table.
Remove unnecessary include.
Merge pull request #83 from Juniper/nsheth_evpn_origin_vn

Add OriginVn support for Evpn routes.

Looks good Nischal. One Q: Is there any upgrade issue here. I presume older code for enet routes received via bgp may not have originVn attribute ?

Thanks,
Ananth