Add missing project argument to gcloud commands

To allow a project to be specified in config-default.sh for the GCE platform we need to make sure this project environment variable is propagated to all the gcloud commands that need them, otherwise kube-up.sh, kube-down.sh only work for the currently selected project with gcloud config and not the PROJECT enviornment variable. I've just tested this with a kube-up and kube-down for PROJECT=kubernetes-satnam2 while the gcloud config default project was set to something else and it seemed to work fine.

@jbeda