BUG-1288: improve InstanceIdentifier API

Introduces getLastPathArgument and getReversePathArguments, which are
useful for some users, who open-code the equivalent methods.

Also removes the use of deprecated constructor, opting for an Iterables
utility class for intering instantiation.

Change-Id: I364e41dc7efdd1b3c56d03e626c8671b2c20ae8d
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "BUG-1288: improve InstanceIdentifier API"