OVSDB SB model for port and interface

OVSDB SB model for port and interface

Initial augmentation of termination-point to add
OVSDB port and interface support.  No doubt additional
fields will need to be added.

Looking for feedback on the approach.

v2 - flatten out the model so both ovsdb port and interface
attributes will be present in the ovsdb termination-point
augmentation.  More attributes to be added.

v3 - use identity types for the interface type

Change-Id: Ifbff6060c8f6dae3caa49c43fbaf18e5060031b1
Signed-off-by: Eric Multanen <eric.w.multanen@intel.com>