Automatic merge from submit-queue

AWS kube-up: tolerate a lack of ephemeral volumes

Some users have requested the ability to _not_ use ephemeral volumes (local instance storage), but this also highlighted the fact that we likely fail to start on instance types with no instance storage (e.g. the c4 class instances).

Confirming this fix, and then going to confirm that e.g. c4 is broken.  If so this will be a cherry-pick candidate.