Better fix of #212

The manifest-from-url feature of kubelet will now accept either single or arrays of manifests.

I'm adding a bit to integration test that makes sure our container vm guestbook example causes a container to be created. Right now I'm just pulling it from https://raw.githubusercontent.com/GoogleCloudPlatform/container-vm-guestbook-redis-python/master/manifest.yaml every time. Do you think I should cache it locally? I kind of like pulling it every time because that ensures that our documentation and reality will stay aligned, but it also makes the test depend on github...
I prefer that form when the side effects of the call are logically bound up with the body of the if statement. I can change it if you feel especially strongly.