Updated openstack/openstack
Project: openstack/neutron  b9e03424e291c512a30416973044b13c097eb060

NSX: do not raise on missing router during migration step

Return None for missing router rather raising NotFound exception;
this is what the client code was expected to handle in the first
place.

Closes-bug: 1313918

Change-Id: I573770a69d0170b027fc990c29aaa87b1fc8eccc