Sets up Travis CI tests to use a Kubernetes cluster on GKE. All tests have access to $KUBECONFIG which points at a kubeconfig file with credentials to a cluster.
I had to skip the poolmgr unit test because it currently assumes NodePort services; that will be fixed in another change.
Also, because some of the tests don't work properly in parallel, I've ended up reducing the concurrency to 1. If this becomes a problem we'll have to fix the tests, but for now I don't mind just waiting a few minutes longer.
