Make e2e shell tests work standalone

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.)

hack/e2e-suite/pd.sh

@@ -22,8 +22,17 @@ set -o nounset
 set -o pipefail
 
 KUBE_ROOT=$(dirname "${BASH_SOURCE}")/../..
+
+: ${KUBE_VERSION_ROOT:=${KUBE_ROOT}}
+: ${KUBECTL:="${KUBE_VERSION_ROOT}/cluster/kubectl.sh"}
+: ${KUBE_CONFIG_FILE:="config-test.sh"}
+
+export KUBECTL KUBE_CONFIG_FILE
+
 source "${KUBE_ROOT}/cluster/kube-env.sh"
-source "${KUBE_ROOT}/cluster/$KUBERNETES_PROVIDER/util.sh"
+source "${KUBE_VERSION_ROOT}/cluster/${KUBERNETES_PROVIDER}/util.sh"
+
+prepare-e2e
 
 if [[ "$KUBERNETES_PROVIDER" != "gce" ]] && [[ "$KUBERNETES_PROVIDER" != "gke" ]]; then
   echo "WARNING: Skipping pd.sh for cloud provider: ${KUBERNETES_PROVIDER}."