BUG-865: do not use InstanceIdentifier.getPath()

InstanceIdentifier exposes the reverse path via a dedicated method, so
use that rather than home-brewing our own.

Change-Id: I3568bf8fc294e235a9f5bae8a72d6cd89079b348
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "BUG-865: do not use InstanceIdentifier.getPath()"