BUG-1287: migrate bgp-topology-provider

Data store has a new set of APIs, which are more efficient. This is a
straightforward migration, without taking advantage of the full APIs
available.

Change-Id: I5d82dd8ed0cb95f2075593713f253bd9abc5b686
Signed-off-by: Robert Varga <rovarga@cisco.com>
Signed-off-by: Milos Fabian <milfabia@cisco.com>