Add uuid to Port DB model.

This patch adds uuid column to ports table.
Fixes: bug #1190916

Change-Id: Ie7a7c1150a863ee42f382eaf1393a2e3961434df
Create Port object.

1. Added the model of a Port.
2. Defined __all__ for ironic.objects to simplify
   accessing the models.
3. Made @objectify universal for all objects.

Partially implements blueprint: ironic-object-model

Change-Id: Iec88310811d0e17903b5182d08e293dd4d0967d0
Merge "Add uuid to Port DB model."
Merge "Create Port object."