Simply incorporate some of the boilerplate from hack/e2e.go into the
scripts in hack/e2e-suite.

Use environment variables with default values to allow overrides in
kubectl command line and to use a versioned package root.

Tested:
- Ran `go run hack/e2e.go -test` on a test cluster.
- Ran the test cases individually.
- Ran hack/e2e-suite/goe2e.sh -t Pods to confirm it takes arguments.
- Also fixed cluster/test-network.sh (which should be more and more irrelevant.)