webcore: Control server lifetime
webcore: Control server lifetime

We now only start the server at GoingUp time, and we explicitly request
that it shut down at GoingDown time.

MurphyMc/pox,pthien92/sdn,pthien92/sdn,pthien92/sdn,noxrepo/pox,MurphyMc/pox,pthien92/sdn,noxrepo/pox,MurphyMc/pox,noxrepo/pox,pthien92/sdn,noxrepo/pox,MurphyMc/pox,MurphyMc/pox