Ensure port get works when NVP mapping not stored in Quantum DB

Bug 1153616

If the entry for the mapping between a quantum and a NVP port identifier
is not found in the Quantum DB, search the port on NVP, and, if found,
add the mapping entry.
This ensures upgraded folsom databases keep working with Grizzly code.

Change-Id: I74943e8271f522dcd21c1c34b0159dd61bb66e76
Merge "Ensure port get works when NVP mapping not stored in Quantum DB"