Bug 949: Fixed support for DataChangeListeners listening directly on Augmentation

Used InstanceIdentifier codec does not support AugmentIdentifier, since it is
designed for CompositeNode format (serialization as defined by YANG Spec).
Instance Identifier for NormalizedNode format allows to directly reference
augmentation, for which support was missing.

Added a special case handling of Instance Identifiers which targets augmentation
directly, since Binding-Aware API and NormalizedNode API allows it.

Change-Id: I6371a54dae0e32cac4e1c9b9ab309e91ec3192d9
Signed-off-by: Tony Tkacik <ttkacik@cisco.com>