Separate NVP create lport operation and neutron db transaction

Bug 1200001

This patch removes the NVP call for creating a logical port from
the SQL transaction context used for creating the Neutron port.
It also ensures orphaned data are properly removed from both
the Neutron DB and the NVP backend.

Change-Id: I028a1493ecf732f2422e0eaa2020bac4ebdbb457
Merge "Separate NVP create lport operation and neutron db transaction"