GC-150: Fix issues with migration across L2 networks.

Our route parsing was very bad. This santizes it by eating the
"via <gateway>" portion of the output, so that we can still bind
to the correct interface.

Change-Id: I4b2283d4cb4a10df07d393fff0f4cd111d960c5f
Merge remote-tracking branch 'origin/grizzly/1.4' into grizzly15

Conflicts fixed:
	cobalt/nova/extension/manager.py

Change-Id: I9904a24586215c750d1d7c8a741c57f67061d70a