Add local identifier and local AS to BgpNeighborConfig.

A change in the local identifier or local AS for the
bgp-router triggers an update of all the bgp-peerings,
which in turn triggers update of BgpNeighborConfigs.

Add tests to verify that changes to identifier and AS
in the bgp-router are propagated to BgpNeighborConfigs.
Merge pull request #620 from Juniper/nsheth_neighbor_config

Add local identifier and local AS to BgpNeighborConfig.