In order to re-attach the router and make it work in awsvpc mode,
the following has to be done:
- expose_ip on the router
- adjusting arp settings
- restoring host routes
To detect that we run in awsvpc mode, we inspect cmd parameters
of the weave router instead of GET'ing /ipinfo/tracker. This is so,
because the HTTP server started by the router might not be running
at the time of restoration.