Bug 5685: Integate BGP topology provider with cluster singleton service.

Bug 5685: Integate BGP topology provider with cluster singleton service.

The BgpTopologyDeployer service is responsible for a topology builder instances creation.
In clustered environment, this service is running on all three nodes, consuming the same
configuration, create the same topology builder instance and register it to the cluster singleton service
provider on all nodes, but only one instance become active.
This integration allows fail-over scenarios and avoids confilicting datastore modifications for
topology builders with the same topology-id.
Provide backwards compatility for CSS modules, where instance is created and configuration
is written to DS when instance become active.

Change-Id: Id1af5368f5d9fad04243e2ab909c5948632626d7
Signed-off-by: Milos Fabian <milfabia@cisco.com>