Allow to clear extra routes in NVP
Allow to clear extra routes in NVP

Since the neutron client can unset any attribute, ensure
we can handle empty routes as a way to clear the extraroutes
for the router.

Fixes bug #1202890

Change-Id: Ib240a42ba1075d9a410da904b3d3ae9e19b2d86e

gkotton/vmware-nsx,gkotton/vmware-nsx