Refactor GCE wrapper library to allow execution from E2E test suite

This reverts commit 147b6911f5, reversing
changes made to 6fd986065b.

hack/ginkgo-e2e.sh

@@ -97,6 +97,7 @@ export PATH=$(dirname "${e2e_test}"):"${PATH}"
   --provider="${KUBERNETES_PROVIDER}" \
   --gce-project="${PROJECT:-}" \
   --gce-zone="${ZONE:-}" \
+  --gce-service-account="${GCE_SERVICE_ACCOUNT:-}" \
   --gke-cluster="${CLUSTER_NAME:-}" \
   --kube-master="${KUBE_MASTER:-}" \
   --cluster-tag="${CLUSTER_ID:-}" \