Fix NSX migration path

The migration path for the NSX plugin was not working correctly,
as two migrations (extra route and network gateways) were
skipped.
Therefore installations were partially relying on automatic
schema generation.

This patch fixes the migration path, as well as an attribute
whose name in the migration and the DB model differed.

Closes-Bug: 1285095

Change-Id: I9e4db294e618d1419d86e07cfb5505dcc01b54ca
Merge "Fix NSX migration path"