Tweak BgpPeerNotification log to display TCP endpoint if there's no Peer.

Add tests to exercise the code that sends a Notification when BgpPeer is
marked deleted or is being closed.
Add test for deferred peer close.
Avoid timer cancel deadlock
Fix build
Remove copyright
Add RoutepathReplicator test to verify instance route target update.
Add another test where the target goes away and new one is added later.