Bug 4488: Metadata not available for modification NodeModification

Bug 4488: Metadata not available for modification NodeModification

To resovle tis race condition problem, modify EffectiveRibInWriter to
work on per peer basis instead of a global per RIB instance.
The EffectiveRibInWriter is now listening on paricular peer's AdjRibIn tables.
The writer is started when a session goes up and closed when the session goes down.
Peer role is not tracked via data changes rather directly set at creation.

The possitive side effect is better error recovery in a case of failure in
EffectiveRibInWriter.
Disadvantage of this change is tighter coupling between components
(peer, eff-rib-in writer and policy tracker).

Change-Id: I07c6c1e2f864b12c50308c7be75b7faa8cc20c12
Signed-off-by: Milos Fabian <milfabia@cisco.com>