BUG-592: use new InstanceIdentifier APIs

This patch gets rid of deprecation warnings stemming from changes to
InstanceIdentifier APIs. These have been optimized to elide as many
list copies as possible and expose utility functions which are very
useful for building temporary instance identifier objects. We attempt to
use them as much as possible.

Change-Id: I7cd8e116eaf2080974ba6d943279f6586298ca50
Signed-off-by: Robert Varga <rovarga@cisco.com>