BUG-1023: fix warnings emitted during loading of OF13 models

This fixes a thinko when multiple entities exist with the same base
schema path.

Also reformats the file, adds final keywords and logging which was used
to find the problem. Finally it cleans up exception formatting to
improve readability.

Change-Id: Iab6b7959d7a305bf790d5ca38ad5f4452b185987
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "BUG-1023: fix warnings emitted during loading of OF13 models"