refactor(Vagrantfile): NUM_INSTANCES variable would return 0 if not set
refactor(Vagrantfile): NUM_INSTANCES variable would return 0 if not set

chourobin/weave-demos,chourobin/weave-demos,pierreozoux/guides,matsubo/coreos-vagrant-docker-compose,errordeveloper/weave-demos,errordeveloper/weave-demos,pierreozoux/guides,pessoa/guides,amouat/fleet-vagrant,monkey-H/nap-vagrant,pierreozoux/guides,chourobin/weave-demos,ianblenke/coreos-vagrant-kitchen-sink,rotespferd/coreos-vagrant,cornelius-keller/coreos-vagrant-tinc,oveits/coreos-vagrant,pierreozoux/guides,kcyeu/coreos-vagrant,kikkomep/guides,pierreozoux/guides,triple-i/coreos-vagrant,kikkomep/guides,owlab-exp/coreos-vagrant-devel,andrewrothstein/coreos-vagrant,2yoshi/docker-test,lukebond/etcd-vagrant,pessoa/guides,phamviet/coreos-vagrant-es-cluster,pierreozoux/guides,pierreozoux/guides,triple-i/coreos-vagrant,kikkomep/guides,pierreozoux/guides,phamviet/coreos-vagrant-es-cluster,errordeveloper/weave-demos,pdxjohnny/coreos-vagrant,kikkomep/guides,kikkomep/guides,sjackman/coreos-vagrant,quantum/coreos-vagrant,glevand/coreos--coreos-vagrant,monkey-H/nap-vagrant,somespider/vm,chourobin/weave-demos,kikkomep/guides,kcyeu/coreos-vagrant,leandrocp/coreos-vagrant,oveits/coreos-vagrant,matsubo/coreos-vagrant-docker-compose,errordeveloper/weave-demos,fgbreel/coreos-vagrant-kitchen-sink,j0rdn/coreos-rancher-vagrant,fgbreel/coreos-vagrant-kitchen-sink,kikkomep/guides,kikkomep/guides,ianblenke/coreos-vagrant-kitchen-sink