Add BGPVPN service driver without rpc

[Ofer Ben-Yacov]

In order to provide BGP-VPN functionality when using SDN controller, such as Dragonflow, we can avoid sending messages to local rpc agents to configure the connection between the local and remote networks. Instead, we use the bagpipe post commit mechanism to configure the local connection by populating the SDN controller database.

Suggested implementation will be submitted for review asap.

[Ofer Ben-Yacov (ofer-benyacov)]

This bug complements dragonflow BGP-VPN implementation: https://bugs.launchpad.net/dragonflow/+bug/1733177

[Thomas Morin (tmmorin-orange)]

Indeed, to realize a dragonflow implementation of BGPVPN API, the behavior needed is different than the one of the 'bagpipe' driver for BGPVPN. The BGPVPN driver framework already has everything in place to create a dragonflow driver without any dependency on the existing 'bagpipe' driver: subclassing the BGPVPNDriver [1] class is sufficient to have access to all the postcommit hooks, and interact with bagpipe-bgp from there.

Unless I missed something and the dragonflow driver would need to inherit some particular behavior from the existing bagpipe service plugin... ? If so, then we'd need to identify exactly which pieces would be reused.

[1] https://github.com/openstack/networking-bgpvpn/blob/master/networking_bgpvpn/neutron/services/service_drivers/driver_api.py#L246